p39, a major baculovirus structural protein: immunocytochemical characterization and genetic location.

A series of monoclonal antibodies was produced against proteins from polyhedra-derived virions of the multicapsid nuclear polyhedrosis virus of Orgyia pseudotsugata (OpMNPV). Two of these antibodies (214 and 236) reacted with a protein of 39 kDa on Western blots of electrophoretically separated OpMNPV viron proteins derived from both budded and polyhedra-derived virions. This protein appears to be a major component of both BV and PDV. One of the p39 antibodies was used to characterize p39 synthesis in infected Lymantria dispar cells by using Western blots and immunofluorescent staining. The p39 protein was detected by immunofluorescence microscopy at 24 hr postinfection. By 48 hr, p39 was detected primarily in cell nuclei with little or no detectable staining of the cytoplasm. The two MAbs were used to identify three immunoreactive clones from a lambda gt11 expression library of OpMNPV DNA. By hybridization of insert DNA from three lambda gt11 clones to blots of restriction digests of OpMNPV genomic DNA, the location of the 39-kDa gene was mapped on the OpMNPV genome. Using the lambda gt11 insert DNAs and the monoclonal antibodies, the p39 genes and proteins of OpMNPV and Autographa californica NPV (AcMNPV) were shown to be closely related in size, DNA sequence, and antigenicity. One of the p39 monoclonal antibodies cross-reacted with a host cell protein associated with the condensed chromosomes present during mitosis.