How many rna strands are there

In addition to nuclear DNA, some DNA is present in energy-producing mitochondria, small organelles found free-floating in the cytoplasm, the area of the cell outside the nucleus. The three types of RNA are found in different locations. If it receives the correct signal from the ribosome, it will then hunt down amino acid subunits in the cytoplasm and bring them to the ribosome to be built into proteins 5. Ribosomes are formed in an area of the nucleus called the nucleolus, before being exported to the cytoplasm, where some ribosomes float freely.

Other cytoplasmic ribosomes are bound to the endoplasmic reticulum, a membranous structure that helps process proteins and export them from the cell 5. Meet The Author. Ruairi J Mackenzie.

Chosen for you. Deoxyribonucleic Acid. Ribonucleic Acid. DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism.

RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories. DNA consists of two strands, arranged in a double helix. The Dscam gene of Drosophila , which encodes proteins involved in guiding embryonic nerves to their target destinations during formation of the fly's nervous system, exhibits an especially impressive number of alternative splicing patterns.

Dozens of different forms of Dscam mRNAs and corresponding proteins have been identified, while analysis of the gene's sequence reveals a staggering 38, potential additional mRNAs, based on the large number of introns found.

The ability to produce so many different proteins from a single gene may be necessary for forming as complex a structure as the nervous system Schmucker et al. In general, the existence of multiple mRNA transcripts from single genes may account for the complexity of some organisms, such as humans, even though these organisms have relatively few genes in the case of humans, approximately 25, Figure 7: Introns are removed during RNA splicing.

Non-coding sequences, or introns, are removed during RNA splicing to produce a mature mRNA transcript composed of exons coding sequences. Genetics: A Conceptual Approach , 2nd ed. All rights reserved.

Most types of cells possess approximately 30 to 40 different tRNAs, with more than one tRNA corresponding to each amino acid. Structural studies using X-ray crystallography have demonstrated that the cloverleaf is further folded into an L shape Figure A loop at one end of the folded structure base-pairs with three nucleotides on the mRNA that are collectively called a codon ; the complementary three nucleotides on the tRNA are called the anticodon.

Figure Although the pairing between codon and anticodon takes place over three nucleotides, strict complementary base-pairing is only necessary between the first two nucleotides. The third position is referred to as the " wobble " position Figure 11 , and the rules for base-pairing are less stringent at this position.

The discovery of these RNAs has been one of the most exciting advances in recent years, and there is currently a lot of interest in the use of these molecules as possible therapies. But as far as their structure is concerned, these RNAs all share the same basic single-stranded chemical structure with, in some cases, higher-order structures obtained through complementary base-pair folding.

New functions for RNA, new modifications to RNA, and other surprises undoubtedly await discovery in the years to come. Figure The "wobble" position. This base-pairing flexibility is also called "wobble. Berget, S. Spliced segments at the 5' terminus of adenovirus 2 late mRNA. Proceedings of the National Academy of Sciences 74 , — Early, P. Cell 20 , — Evans, R.

Cell 12, — Holley, R. Structure of a ribonucleic acid. Science , — doi Patel, A. Splicing double: Insights from the second spliceosome. Nature 4 , — doi Rich, A. A hybrid helix containing both deoxyribose and ribose polynucleotides and its relation to the transfer of information between the nucleic acids. Proceedings of the National Academy of Sciences 46 , — A new two-stranded helical structure: Polyadenylic acid and polyuridylic acid.

Journal of the American Chemical Society 78 , — link to article. Schmucker, D. Drosophila Dscam is an axon guidance receptor exhibiting extraordinary molecular diversity. Cell , — Theimer, C. Structure of the human telomerase RNA pseudoknot reveals conserved tertiary interactions essential for function. Molecular Cell 17 , — Restriction Enzymes. Genetic Mutation. Functions and Utility of Alu Jumping Genes. Transposons: The Jumping Genes. DNA Transcription. What is a Gene? Key steps inhibited by compounds that are currently being validated and which represent attractive antiviral targets are highlighted in red.

Their development intimately relies on the deepened understanding of basic mechanisms of coronavirus gene functions as well as of the molecular interactions with host factors.

Since the discovery of the first coronavirus avian infectious bronchitis virus in the s 7 and the discovery of the first human coronaviruses HCoVE and HCoV-OC43 in the s 8 , 9 , the coronavirus research field has made substantial progress in understanding the basic principles of coronavirus replication and pathogenesis Box 1. Moreover, the unprecedented speed and technical progress of coronavirus research that has become evident in a few months after the appearance of SARS-CoV-2 at the end of has led to a rapidly growing understanding of this newly emerging pathogen and of its associated disease, COVID In this Review, we discuss key aspects of coronavirus biology and their implications for SARS-CoV-2 infections as well as the treatment and prevention strategies.

Coronaviruses CoVs are a large family of viruses long known to infect a wide variety of mammalian and avian species, including livestock and companion animals. In , the avian infectious bronchitis virus IBV was the first coronavirus to be discovered 7. The following period was essential in the discovery of research milestones that majorly contributed to coronavirus knowledge: polyprotein processing 62 , first full-length coronavirus genome sequence , first recombinant coronaviruses engineered by targeted recombination , , discontinuous transcription 78 , full-length reverse genetic clones , , and electron microscopy of double-membrane vesicles As human-to-human transmission mainly occurred after the onset of symptoms, drastic public health measures, including travel restrictions and isolation of infected patients, succeeded in containing the international spread to limited foyers of infections.

MERS-CoV also originated from bats and established an animal reservoir in dromedary camels , Despite sporadic zoonotic transmissions to humans upon prolonged contact and the limited human-to-human transmission, MERS-CoV infections are still detected Recently, the pathogenic SARS-CoV-2 rapidly spread in the human population after a likely spillover from bats or from a yet unidentified intermediate host 14 , , SARS-CoV-2 targets both upper and lower respiratory tract tissues and efficient human-to-human transmission occurs even before the onset of symptoms 36 , Clinical manifestations range from asymptomatic or mild infections to acute lung inflammation and pneumonia, mostly in the elderly and patients with comorbidities 36 , , Coronavirus S proteins are homotrimeric class I fusion glycoproteins that are divided into two functionally distinct parts S1 and S2 Fig.

The surface-exposed S1 contains the receptor-binding domain RBD that specifically engages the host cell receptor, thereby determining virus cell tropism and pathogenicity.

The transmembrane S2 domain contains heptad repeat regions and the fusion peptide, which mediate the fusion of viral and cellular membranes upon extensive conformational rearrangements 10 , 11 , The cleavage sites are indicated.

The colour code designates conserved spike regions surrounding the angiotensin-converting enzyme 2 ACE2 -binding domain among severe acute respiratory syndrome-related coronaviruses SARSr-CoVs and high amino acid sequence variations within the site of receptor interaction.

The alignment was coloured according to percentage amino acid similarity with a Blosum 62 score matrix. The colour code designates conserved spike regions surrounding the ACE2-binding domain among SARSr-CoVs and high amino acid sequence variations within the site of receptor interaction. The spike contact residues for ACE2 interaction are marked with asterisks. These data suggest that, much like during the evolution of SARS-CoV, frequent recombination events between severe acute respiratory syndrome-related coronaviruses that coexist in bats probably favoured the emergence of SARS-CoV-2 ref.

Indeed, predicted recombination breakpoints divide the S gene into three parts. However, the amino-terminal and carboxy-terminal parts of the SARS-CoV-2 S protein amino acids 1—1, and 1,—3,, respectively are more closely related to severe acute respiratory syndrome-related coronaviruses ZC45 and ZXC These observations highlight the importance of recombination as a general mechanism contributing to coronavirus diversity and might therefore drive the emergence of future pathogenic human coronaviruses from bat reservoirs.

This emphasizes the need for surveillance to determine the breadth of diversity of severe acute respiratory syndrome-related coronaviruses, to evaluate how frequently recombination events take place in the field and to understand which virus variants have the potential to infect humans.

Increased surveillance is thus instrumental to improve our preparedness for future outbreaks of severe acute respiratory syndrome-related coronaviruses. Besides receptor binding, the proteolytic cleavage of coronavirus S proteins by host cell-derived proteases is essential to permit fusion 24 , These data support the evaluation of the TMPRSS2 inhibitors camostat mesylate and nafamostat mesylate in clinical trials, since in vitro studies have demonstrated their potent antiviral activity against emerging coronaviruses, including SARS-CoV-2 refs 29 , 31 , SARS-CoV primarily targets pneumocytes and lung macrophages in lower respiratory tract tissues, where ACE2 is predominantly expressed, consistent with the lower respiratory tract disease resulting from SARS-CoV infection and the limited viral spread 33 , 34 , Cleavage results in enhanced infection and has been proposed to be a key event in SARS-CoV-2 evolution as efficient S protein cleavage is required for successful infection and is a main determinant in overcoming species barriers 10 , 11 , 12 , 15 , 16 , 28 , 30 , 44 , 45 , This pre-processing of the SARS-CoV-2 S protein by furin may contribute to the expanded cell tropism and zoonotic potential and might increase transmissibility 16 , Importantly, such cleavage sites have not been identified in other members of the Sarbecovirus genus However, there are multiple instances of furin-like cleavage site acquisitions that occurred independently during coronavirus evolution and similar cleavage sites are present in other human coronaviruses such as HCoV-HKU1 ref.

Recently, an independent insertion of amino acids PAA at the same region of the S protein has been identified in the bat coronavirus RmYN02 ref. Such independent insertion events highlight the zoonotic potential of bat severe acute respiratory syndrome-related coronaviruses and may increase the possibility of future outbreaks. The importance of coronavirus S protein-mediated receptor binding and temporally coordinated conformational rearrangements that result in membrane fusion make this process a prime target of innate and adaptive antiviral responses.

Notably, a screen involving several hundred interferon-stimulated genes identified lymphocyte antigen 6 family member E Ly6E as a potent inhibitor of coronavirus fusion Ly6E-mediated inhibition of coronavirus entry was demonstrated for various coronaviruses, including SARS-CoV-2, and seems to have pivotal importance in protecting the haematopoietic immune cell compartment in a mouse model of coronavirus infection.

Moreover, the exposure of S protein on the surface of the virion results in the induction of specific neutralizing humoral immune responses Coronavirus S proteins are heavily glycosylated, which promotes immune evasion by shielding epitopes from neutralizing antibodies 16 , 53 , Several specific or cross-reactive antibodies that bind the SARS-CoV-2 S protein have been recently reported and their administration to infected patients could potentially provide immediate protection 55 , 56 , 57 , Taken together, the exploitation of a combination of multiple neutralizing antibodies that do not compete for overlapping epitopes may not only result in synergistic improvements but also impede the appearance of escape mutations.

Sequence identity differed highly upon comparison of individual genes and domains, indicating frequent recombination events in natural reservoir hosts 14 , 23 , Moreover, the environmental separation of bats and humans might favour the existence of an intermediate host, responsible for SARS-CoV-2 adaption and transmission into the human population, just like civet cats were suggested in the SARS-CoV outbreak The example of pangolin CoV MP, which shared five essential amino acids for ACE2 binding in the S with SARS-CoV-2 highlights the existence of a variety of unidentified betacoronaviruses in wild-life animals and their roles as possible intermediate hosts The release of the coronavirus genome into the host cell cytoplasm upon entry marks the onset of a complex programme of viral gene expression, which is highly regulated in space and time.

This determines the stoichiometry between pp1a and pp1ab, with pp1a being approximately 1. Sixteen non-structural proteins are co-translationally and post-translationally released from pp1a nsp1—11 and pp1ab nsp1—10, nsp12—16 upon proteolytic cleavage by two cysteine proteases that are located within nsp3 papain-like protease; PL pro and nsp5 chymotrypsin-like protease Fig.

The protease residing in nsp5 is frequently referred to as 3C-like protease 3CL pro , because of its similarities to the picornaviral 3C protease, or as main protease M pro , because it is responsible for proteolytic processing of the majority of polyprotein cleavage sites. Proteolytic release of nsp1 is known to occur rapidly 62 , which enables nsp1 to target the host cell translation machinery 63 , 64 , Nsp2—16 compose the viral RTC and are targeted to defined subcellular locations where interactions with host cell factors determine the course of the replication cycle 66 , 67 , Nsp2—11 are believed to provide the necessary supporting functions to accommodate the viral RTC, such as modulating intracellular membranes, host immune evasion and providing cofactors for replication, whereas nsp12—16 contain the core enzymatic functions involved in RNA synthesis, RNA proofreading and RNA modification 4 , Coronavirus polyprotein processing and domains of non-structural proteins nsp are illustrated for severe acute respiratory syndrome-related coronaviruses.

Proteolytic cleavage of the polyproteins pp1a and pp1ab is facilitated by viral proteases residing in nsp3 PL pro and nsp5 M pro. PL pro proteolytically releases nsp1, nsp2, nsp3 and the amino terminus of nsp4 from the polyproteins pp1a and pp1ab indicated by the blue arrows. M pro proteolytically releases nsp5—16 and the carboxy terminus of nsp4 from the polyproteins pp1a and pp1ab indicated by the red arrows Conserved domains and known functions are schematically depicted for nsp1—16 refs 4 , 66 , 67 , One such target is M pro , which resides in nsp5.

M pro releases the majority of nsps from the polyproteins and is essential for the viral life cycle. Furthermore, as M pro is very sequence specific, compounds that structurally mimic those cleavage sites can specifically target the viral protease with little or no impact on host cellular proteases 75 , 76 , Based on structural analysis of the protein, multiple research groups have successfully developed lead compounds that block M pro function in cell culture assays, thus providing frameworks that could aid in rapid drug discovery 75 , Viral genomic replication is initiated by the synthesis of full-length negative-sense genomic copies, which function as templates for the generation of new positive-sense genomic RNA.

These newly synthesized genomes are used for translation to generate more nsps and RTCs or are packaged into new virions. The discontinuous step of negative strand RNA synthesis results in the production of a set of negative-strand sgRNAs that are then used as templates to synthesize a characteristic nested set of positive-sense sg mRNAs that are translated into structural and accessory proteins.

Schematic depiction of coronaviral RNA synthesis. This process can take place at any TRS-B and will collectively result in the production of the characteristic nested set of coronaviral mRNAs. However, it remains to be determined whether all of these non-canonical sgRNAs truly arise by discontinuous transcription or whether they represent RNAs that result from recombination.

Nevertheless, similar findings were previously reported for other coronaviruses, including MHV 61 and HCoVE 81 , which indicates an enhanced coding potential for coronaviruses Overall, these unexpected fusion events may drive coronavirus evolution through variant generation, and novel ORFs could encode additional accessory proteins that are involved in either viral replication or modulation of the host immune response 60 , The RdRP residing in nsp12 is the centrepiece of the coronavirus RTC and has been suggested as a promising drug target as it is a crucial enzyme in the virus life cycle both for replication of the viral genome but also for transcription of sgRNAs.

The structural similarities of the RdRP active site, including conserved key amino acid residues, with other positive-sense RNA viruses suggest the possibility to repurpose known drugs that are effective against other RNA viruses One of the most promising candidates is the phosphoramidate remdesivir RDV , which, in its triphosphate form, acts as a substrate for viral RdRPs and competes with ATP In contrast to classic nucleoside analogues that lead to immediate termination of the synthesis reaction after incorporation, the RdRP continues for three nucleotides after RDV has been incorporated before chain termination.

Nucleotide analogues like RDV may have limited efficacy owing to the proofreading function of the exonuclease domain contained in nsp14 ExoN The corrective function that is exerted by ExoN is not only responsible for maintaining the stability of the coronavirus genome but also enables the excision of erroneous mutagenic nucleotides 71 , The mode of action observed for RDV might be an explanation for its increased efficiency over other nucleoside analogues as the delayed-chain termination could lead to improved evasion from the proofreading function of nsp The current model suggests steric hindrance as a likely reason for termination, disturbing the positioning of the RNA and thus hampering the translocation to the next position 86 , However, a recent randomized, double-blind, placebo-controlled clinical trial in humans with severe COVID showed limited clinical efficacy of RDV treatment 92 and further studies will be necessary.

Another promising candidate is the purine analogue favipiravir FPV , which has been shown to effectively target multiple RNA viruses Although the mechanism of action is not yet completely understood, a recent study of the in vitro mechanism of FPV suggested a combination of chain termination, slowed RNA synthesis and lethal mutagenesis as the mode of action against SARS-CoV-2, which indicates that FPV might be used to effectively restrict viral replication Indeed, results of an experimental pilot study showed that using FPV as treatment against COVID led to increased recovery and faster viral clearance times in treated patients compared to control treatments Clinical studies with both RDV and FPV are currently ongoing and will establish whether these compounds are effective antivirals to treat coronavirus infections The structural proteins of SARS-CoV-2 have not yet been assessed in terms of their role in virus assembly and budding.

In general, coronavirus structural proteins assemble and assist in the budding of new virions at the endoplasmic reticulum ER -to-Golgi compartment that are suggested to exit the infected cell by exocytosis 95 , 96 , During this process, viral interference with lysosomal acidification, lysosomal enzyme activity and antigen presentation was demonstrated.

In addition, ORF10 has been postulated to be located downstream of the N gene. For example, in the case of ORF10, recent sequencing data questioned whether ORF10 is actually expressed, as the corresponding sgRNA could only be detected once in the entire dataset Furthermore, using proteomics approaches, the ORF10 protein has not been found in infected cells , , whereas ribosome profiling data suggested that ORF10 may be translated The accessory genes display a high variability among coronavirus groups and usually show no sequence similarity with other viral and cellular proteins.

Although they are not required for virus replication in cell culture 4 , 5 , they are, to some extent, conserved within the respective virus species and are suspected to have important roles in the natural host. Although there are indications that ORF3b could exhibit its interferon antagonistic function also in a truncated form 99 , it has not yet been found to be expressed at the protein level in virus-infected cells , Whereas the early isolates from human patients contained a full-length ORF8, a deletion of 29 nucleotides was observed in all SARS-CoV strains during the middle-to-late stages.

Furthermore, less frequent deletion events were also observed, including an nucleotide deletion and a nucleotide deletion, which led to a complete loss of ORF8 refs , , suggesting a possible benefit of SARS-CoV ORF8 deletions in vivo. This may indicate a tendency towards host adaption and decreased pathogenicity or, alternatively, that the ORF8 protein is dispensable in humans, whereas it is required in the natural host.

Primary interactions between nsps and host cell factors during the early coronavirus replication cycle initiate the biogenesis of replication organelles 66 , , Although mechanisms underlying replication organelle formation are not fully understood, the concerted role of the membrane-spanning nsp3, nsp4 and nsp6 has been implicated in diverting host endomembranes into replication organelles , , Detailed electron microscopy investigations have described the phenotypic appearance and extent of membrane modifications induced by coronaviruses to accommodate viral replication.

Coronavirus infection, like many other positive-sense RNA viruses, manifests in the generation of ER-derived and interconnected perinuclear double-membrane structures such as double-membrane vesicles DMVs , convoluted membranes and the recently discovered double-membrane spherules , , , Interestingly, these structures are highly dynamic and develop during the viral life cycle , Even though replicase subunits — notably SARS-CoV nsp3, nsp5 and nsp8 — have been shown to be anchored on convoluted membranes, to date, the specific location of viral RNA synthesis remains the most intriguing unanswered question , Although, until recently, no openings towards the cytosol have been observed 97 , , molecular pores involving nsp3 were demonstrated to span DMVs in MHV-infected cells These newly identified structures, which were also observed in SARS-CoVinfected cells, provide a connection between the dsRNA-containing DMV interior and the cytosol, thereby hypothetically rendering newly synthesized viral RNAs available for translation and encapsidation into nascent virions They also provide new opportunities to experimentally address the origin, fate and trafficking routes of viral RNAs contained in DMVs.

Replication organelles are a conserved and characteristic feature of coronavirus replication and, consistent with suggested roles of rewired intracellular membranes in the context of other positive-sense RNA virus infections, they provide a propitious niche with adequate concentrations of macromolecules necessary for RNA synthesis while preventing the exposure of viral replication intermediates to cytosolic innate immune sensors 95 , The functional dissection of coronavirus replication organelles has proven challenging as their contributions to viral fitness and pathogenesis are indistinguishable from functions provided by enzymes of the RTC, which are anchored on the membranes of the replication organelle , , Nevertheless, recent studies revealed the overall composition of the coronavirus RTC, with nsp2—nsp16 and the nucleocapsid protein comprising the viral components 68 , Moreover, several genetic and proteomic screening approaches aimed at deciphering essential coronavirus—host interactions and the RTC microenvironment identified supportive roles of the ER and the early secretory system as well as related vesicular trafficking pathways for efficient replication 68 , , , and provided a comprehensive list of cellular proteins that are in close proximity to the coronaviral RTC 68 , , , Collectively, these studies, in combination with advanced electron microscopy, provide ground for future studies to dissect the microarchitecture of the coronaviral RTC in relation to remodelled ER-derived membranes and to functionally link those structures to processes taking place in close proximity to the RTC such as translation, replication and transcription of viral RNA.

A successful intracellular coronavirus life cycle invariably relies on critical molecular interactions with host proteins that are repurposed to support the requirements of the virus. This includes host factors required for virus entry such as the entry receptor and host cell proteases , factors required for viral RNA synthesis and virus assembly such as ER and Golgi components and associated vesicular trafficking pathways and factors required for the translation of viral mRNAs such as critical translational initiation factors 68 , , , , , , A first systematic expression study of SARS-CoV-2 proteins and subsequent affinity purification followed by mass spectrometry identified more than potential coronavirus—host protein interactions.

These systematic screening approaches of large compound libraries that target host proteins provide means of rapidly identifying antiviral repurposed drugs and accelerated clinical availability However, a detailed functional characterization of conserved host pathways that promote coronavirus replication will guide the development of efficacious targeted therapeutics against coronavirus infections.

In addition, coronaviruses efficiently evade innate immune responses. Virus—host interactions in this context are multifaceted and include strategies to hide viral pathogen-associated molecular patterns, such as replication intermediates dsRNA , that may be sensed by cytosolic pattern recognition receptors , The coronaviral RTC also contributes to innate immune evasion through several nsp-encoded functions.

Although these mechanisms have been elucidated in considerable detail for several prototype coronaviruses, data for SARS-CoV-2 are not yet available. Besides the well-conserved functions residing in the nsps that comprise the RTC, additional mechanisms to counteract innate immune responses are known for coronaviruses.

For example, nsp1 is rapidly proteolytically released from pp1a and pp1ab and affects cellular translation in the cytoplasm to favour viral mRNAs over cellular mRNA, and thereby also decreases the expression of type I and III interferons and of other host proteins of the innate immune response.

Indeed, a first structural and functional analysis of SARS-CoV-2 nsp1 showed binding of nsp1 to ribosomes and nsp1-mediated impairment of translation Although this property remains to be demonstrated in the context of viral infection, these results suggest that SARS-CoV-2 shares some preserved accessory protein activities with SARS-CoV that interfere with antiviral host responses.

Thus, there is a need to establish experimental systems, such as representative animal models to study the transmission and pathogenicity of SARS-CoV-2, primary airway epithelial cultures and organoids to study SARS-CoV-2 replication and host responses to infection in relevant cell types, and reverse genetics systems to study the specific gene functions of SARS-CoV-2 Table 1.

As we currently understand, SARS and COVID are a consequence of virus-encoded functions and delayed interferon responses and, in severe cases, they are associated with dysregulated immune responses and immunopathologies , Indeed, rapid and uncontrolled viral replication of SARS-CoV has been demonstrated to evade the host innate immune activation during its initial steps.

As a consequence, the increase in aberrant pro-inflammatory responses and immune cell infiltration in the lungs provoke tissue damage and contribute to the clinical manifestation of SARS Consistently, host responses, such as cytokine expression, that are known to drive inflammation and immunopathologies have been assessed in studies that revealed that SARS-CoV-2 considerably affects the transcriptional landscape of infected cells by inducing inflammatory cytokine and chemokine signatures 38 , , Although interferon responses have been shown to potently impair SARS-CoV-2 replication, only moderate induction of type I interferon, type II interferon and interferon-stimulated genes was reported 38 , Together, these effects may translate into strong and dysregulated pro-inflammatory responses, while cells display low innate antiviral defence activation as revealed by single-cell transcriptomic studies of nasopharyngeal and bronchial patient samples 38 , , , In severe COVID cases, as opposed to mild cases, aberrant recruitment of inflammatory macrophages and infiltration of T lymphocytes, including cytotoxic T cells, as well as of neutrophils have been measured in the lung , The accumulating evidence of dysregulated pro-inflammatory responses during SARS-CoV-2 infections has led to the use of immune modulators to inhibit hyperactivated pathogenic immune responses , , , In contrast to the SARS-CoV epidemic of almost 20 years ago, improved technologies, such as transcriptomics, proteomics, single-cell RNA sequencing, global single-cell profiling of patient samples, advanced primary 3D cell cultures and rapid reverse genetics, have been valuable tools to understand and tackle SARS-CoV-2 infections.

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