Cell-free synthesis of the precursor polypeptide for avian myeloblastosis virus DNA polymerase.

Abstract

High MW RNA (35S) isolated from avian myeloblastosis virus directs the cell-free synthesis of 2 prominent polypeptides of 180,000 and 76,000 MW. The latter polypeptide was previously identified as the precursor to the group-specific antigens of the virus (gag proteins). Two-dimensional tryptic peptide analyses of the [35S]methionine-labeled peptides demonstrate that the 180,000 dalton product is a polyprotein that can account for all the peptides of the avian myeloblastosis virus DNA polymerase (DNA nucleotidyltransferase, EC 2.7.7.7.) and those of the gag viral proteins. This is direct confirmation of the genomic order of the viral structural genes, placing the polymerase gene adjacent to the 5''-proximal gag gene of the virus. The primary polymerase gene product is probably the .beta. subunit of the enzyme. These results are discussed in relation to the proposed structural gene map for the avian retraviruses and suggest a model for the in vivo processing of the viral polymerase.