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Nevertheless, it has been estimated that SARS-CoV-2 undergoes 3×10 –6 mutations per nucleotide per replication cycle. Unlike other RNA viruses, coronaviruses have RNA proofreading machinery to correct genetic mutations due to the 3′-5′ exonuclease activity of nsp14. The nonstructural proteins are involved in viral RNA replication and gene expression, assembling an RNA synthesis complex in which nsp12 functions as an RNA-dependent RNA polymerase. The structural proteins include the spike (S) protein, envelope (E) protein, membrane (M) protein, and nucleoprotein (N).

The SARS-CoV-2 genome is a 29.9-kb positive-sense single-stranded RNA molecule containing 14 ORFs, which encode four structural and 16 nonstructural proteins (nsp 1–16). SARS-CoV-2 is an enveloped, spherical RNA virus that belongs to the genus Betacoronavirus of the family Coronaviridae, order Nidovirales. The outbreak became a pandemic in a short time, and as of 27 July, 2021, there have been nearly 194 million confirmed cases of COVID-19 and over 4 ?million ? deaths reported to WHO. On January 7, a novel coronavirus later named "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2) was implicated as the etiological agent of the outbreak, and the disease was named "coronavirus disease 2019" (COVID-19). A cluster of etiologically unknown pneumonia was reported to the World Health Organization (WHO) by China's health authority on 31 December 2019.