A temperature-sensitive mutant of the baculovirus Autographa californica nuclear polyhedrosis virus defective in an early function required for further gene expression

Fifteen temperature-sensitive (ts) mutants of the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV) have been analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins synthesized in infected cells. One of the mutants, tsB821, was found to be defective in a very early function. Seven virus-induced proteins were synthesized by 2 hr postinfection. In marked contrast to wild-type virus and the other 14 ts mutants, the synthesis of further virus-induced proteins did not occur in tsB821-infected cells at the restrictive temperature (33 degrees ). Host protein synthesis continued as normal after transient expression of the seven early proteins. Viral-specific DNA synthesis was blocked or significantly delayed in tsB821-infected cells at 33 degrees . The relative synthesis of certain viral-induced proteins, particularly P31, P32, P42, P66, and P69, varied considerably in the remaining 14 mutants at 33 degrees. Three mutants exhibited alterations in specific polypeptides; P75 was approximately 1 kDa smaller in tsB1075, P40 was approximately 1 kDa smaller in tsB951, and P25 was greatly reduced in quantity or altered in tsB305.