THE ROLE OF THE ACMNPV 25K GENE, FP25, IN BACULOVIRUS POLH AND P10 EXPRESSION

A previous study showed that an Autographa californica multicapsid nuc lear polyhedrosis virus (AcMNPV) 25K mutant produced less polyhedrin p rotein than wild-type (Jarvis et al., J. Virol. 66, 6903-6911, 1992). In this study, the role of the 25K gene product (AcMNPV ORF 61) in bac ulovirus gene expression was further investigated. Five different vira l 25K mutants expressed lower levels of polyhedrin protein and less CA T activity under the control of the polh promoter compared to wild-typ e. Polh RNA was equally stable in wild-type and mutant virus-infected cells while the rate of polh transcription was significantly reduced i n mutant-infected cells. in comparison, steady-state levels of p10 RNA were not reduced in 25K mutant-infected cells, indicating that the re duction in polh RNA did not reflect a general effect on very late gene transcription. Expression of ie-1, which also appears to influence po lh expression (Choi and Guarino, Virology 209, 90-98, 1995), was not i nfluenced by 25K mutation. These results show that the 25K protein is important for maintaining optimal levels of polh transcription by a me chanism that does not involve maintaining ie-1 expression. (C) 1996 Ac ademic Press, Inc.