CHARACTERIZATION OF A 105-KDA POLYPEPTIDE ENCODED IN GENE-1 OF THE HUMAN CORONAVIRUS HCV 229E

Gene 1 of the human coronavirus HCV 229E encompasses approximately 20. 7 kb and contains two overlapping open reading frames, ORF 1a and ORF 1b. The downstream ORF 1b is expressed by a mechanism involving (-1) r ibosomal frameshifting. Translation of mRNA 1, which is thought to be equivalent to the viral genomic RNA, results in the synthesis of two l arge polyproteins, pp1a and pp1ab. These polyproteins contain motifs c haracteristic of papain-like and 3C-like proteinases, RNA-dependent RN A polymerases, helicases, and metal-binding proteins. In this study, w e have produced pp1ab-specific monoclonal antibodies and have used the m to detect an intracellular, 105-kDa viral polypeptide that contains the putative RNA polymerase domain. Furthermore, using trans cleavage assays with bacterially expressed HCV 229E 3C-like proteinase, we have demonstrated that the 105-kDa polypeptide is released from pp1ab by c leavage at the dipeptide bonds Gln-4068/Ser-4069 and Gln-4995/Ala-4996 . These data contribute to the characterization of coronavirus SC-like proteinase-mediated processing of pp1ab and provide the first identif ication of an HCV 229E ORF lab-encoded polypeptide in virus-infected c ells. (C) 1996 Academic Press, Inc.