nsp8 functions as an RNA-dependent RNA polymerase (RdRp) that serves as the primase for nsp12, the main RdRp of the SARS coronavirus 1 (SARS-CoV-1) (Imbert et al. 2006), as it is capable of de novo RNA synthesis (te Velthuis et al. 2011). nsp8 synthesizes short oligonucleotides (less than 6 bases long) using genomic RNA as a template. nsp8 requires at least one cytidine residue in the template sequence for its activity. Activity is dependent on manganese ions (Imbert et al. 2006). nsp8 can also extend primers but is 20-fold less efficient than nsp12 (te Velthuis et al. 2011).
te Velthuis, AJ,
van den Worm, SH,
RNA-directed 5'-3' RNA polymerase activity of SARS-CoV-1 gRNA:RTC [double membrane vesicle viral factory outer membrane]