The genome and subgenomes of a typical CoV contain at least six ORFs. The first ORFs (ORF1a/b), about two-thirds of the whole genome length, encode 16 nsps (nsp1-16), except Gammacoronavirus that lacks nsp1. There is a -1 frameshift between ORF1a and ORF1b, leading to production of two polypeptides:pp1a and pp1b. These polypeptides are processed by virally encoded  chymotrypsin-like protease (3CL) or main protease (M) and one or two papain-like protease into 16 nsps.