Protein synthesis in BM-N cells infected with Bombyx mori nuclear polyhedrosis virus

Abstract

Polypeptide synthesis in the BM-N cells infected with Bombyx mori nuclear polyhedrosis virus (BmNPV) was examined. At least 26 virus-induced polypeptides were sequentially detected during BmNPV infection when cell extracts pulse-labeled with [ 35S]methionine for 3 hr were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by fluorography. Three virus-induced polypeptides were first detected at 6 hr postinfection (pi) and the synthesis of the majority of virus-induced polypeptides (18 of 26 polypeptides) commenced at 12–18 hr pi. No additional virus-induced polypeptides were detected at 30 hr pi or later. Immunoprecipitation experiments showed that at least 20 virus-induced polypeptides, two of which being unidentified in the pulse labeling experiment without immunoprecipitation, were related to the structural polypeptides of BmNPV virions. Pulse-chase experimets initiated at various times pi showed that at least 12 virus-induced polypeptides disappeared or reduced their radioactivity and at least 16 polypeptides appeared or increased their radioactivity during the chase periods up to 48 hr, suggesting that a number of virus-induced polypeptides underwent post-translational modification. Pulse labeling with N-acetyl-[ 14C]glucosamine and [ 32P]orthophosphate revealed that 6 virus-induced polypeptides were glycosylated and 10 virus-induced polypeptides phosphorylated. In agreement with the results in other NPV species, the polyhedrin of BmNPV were characterized to be a glycophosphoprotein.