SARS‐CoV‐2 is the human coronavirus (CoV) responsible for the CoV disease 19 (COVID‐19) pandemic. Human CoVs are members of the Nidovirales order and belong
to the Coronaviridae family. To date, seven species of human CoVs have been described: HCoV‐NL63, HCoV‐229E, HCoV‐OC43, HCoVHKU1, SARS‐CoV, MERS‐CoV, and
SARS‐CoV‐2. Like other CoVs, SARS‐CoV‐2 is an enveloped virus with a positive‐sense, single‐stranded RNA genome. SARS‐CoV‐2 belongs to the genus betacoronavirus,
together with SARS‐CoV and MERS‐CoV (with 80% and 50% identity, respectively) 
Coronaviruses, including SARS‐CoV‐2, have the largest genomes (26–32 kb) among all of the RNA virus families, which are flanked by 5′ and 3′ untranslated regions. SARS‐
CoV‐2 RNA contains a common ‘leader’ sequence (of 70 nt) . Upon cell entry, the viral genomic RNA (gRNA) is translated to produce nonstructural proteins from two large
open reading frames (ORFs), ORF1a, and ORF1b, via proteolytic cleavage.
Among these, 15 nonstructural proteins make up the viral replication and transcription complex . Of importance, Nsp12 (which harbors RNA‐dependent RNA polymerase; RdRp) leads the
viral replication and transcription mechanisms by using viral RNA as the template.
Fonte: ijms-23-01941 (1)