IDENTIFICATION AND CHARACTERIZATION OF A 65-KDA PROTEIN PROCESSED FROM THE GENE-1 POLYPROTEIN OF THE MURINE CORONAVIRUS MHV-A59

A 65-kDa protein has been detected in mouse hepatitis virus A59 (MHV-A 59)-infected DBT cells using polyclonal antibodies directed against po lypeptides encoded by the 5' 1.8 kb of gene 1. The presence of this 65 -kDa protein (p65) was previously predicted from immunoprecipitation s tudies of gene I expression in MHV-A59-infected DBT cells with other a ntisera (I). p65 was rapidly labeled in virus-infected cells at late t imes of infection; however, its cleavage from the polyprotein was sign ificantly delayed compared to the amino-terminal gene 1 polyprotein cl eavage product, p28. Similar to p28, p65 was cleaved from the growing polyprotein without detectable intermediate precursors. Kinetic analys is of p65 with specific antibodies indicates that p65 is immediately a djacent to p28 in the gene 1 polyprotein. The proteolytic activity res ponsible for the carboxy-terminal cleavage of p65, as well as the func tion of the p65 protein, remains to be determined. (C) 1995 Academic P ress, Inc.