Defective cleavage of a precursor polypeptide in a temperature-sensitive mutant of avian sarcoma virus

Abstract

Noninfectious virus particles released at the nonpermissive temperature from cells infected with the temperature-sensitive mutant LA334 of avian sarcoma virus B77 have been investigated. These particles bud atypically, have improperly formed core structures, are heterogeneous in size and on a density gradient, and are also slightly more dense than wild-type virus. One major new viral-coded protein of 23,000 molecular weight, p23, and several minor abnormally cleaved and/or partially degraded viral-specific peptides are incorporated into the noninfectious particles. As a result of tryptic peptide analyses of some of these new proteins, it could be proposed that the defect of this mutant is in the cleavage of pr76, the 76,000 molecular weight precursor for the internal viral proteins of avian tumor viruses (ATV). In addition, we have detected one methionine-labeled viral tryptic peptide with an altered amino acid composition, which may represent the site of the temperature sensitive lesion.