Meta-Biol

• Pathways

Virally encoded RNA-dependent RNA polymerase (nsp12, also known as RdRP) is the key component of the replication transcription complex (RTC). As the human SARS coronavirus 1 (SARS-CoV-1) is a plus strand RNA virus, nsp12 first synthesizes the complementary minus RNA strand. The purified SARS-CoV-1 nsp12 shows both primer dependent and primer-independent RNA synthesis activities using homopolymeric RNA templates. The catalytic activity of nsp12 is strictly dependent on manganese ions (Mn2+) and primers when the template is a viral-genome-derived RNA representing part of the 3’-UTR of the plus strand with a polyA tail. A 36 nucleotide sequence from the 3’-UTR, predicted to form a stable stem-loop structure, seems to be the minimal cis-acting RNA element required for nsp12 to initiate RNA synthesis (Ahn et al. 2012). The complex of nsp7 and nsp8 confers processivity to nsp12 (Subissi et al. 2014).