Identification and subcellular localization of a 41 kDa, polyprotein 1ab processing product in human coronavirus...

The translation products of the human coronavirus (HCV) 229E open reading frames 1a and 1b, the polyproteins 1a and 1ab, are processed by virus-encoded proteinases. One of the key enzymes in this process is a chymotrypsin-like enzyme, the 3C-like proteinase. In this study we have identified an ORF 1b-encoded, 41 kDa processing product in HCV 229E-infected cells by using a monoclonal antibody with defined specificity. We show that this polypeptide is released from polyprotein 1ab by 3C-like proteinase-mediated cleavage of the peptide bonds Gln-6110/Gly-6111 and Gln-6458/Ser-6459. Also, we have investigated the subcellular localization of the 41 kDa processing product. Immunofluorescence microscopy revealed a punctate, perinuclear distribution of the 41 kDa polypeptide in infected cells and an identical subcellular localization was observed for three additional pp1ab-derived polypeptides. In contrast, the virus nucleocapsid protein showed a homogeneous cytoplasmic localization.