THE STRUCTURAL PROTEIN ODV-EC27 OF AUTOGRAPHA-CALIFORNICA NUCLEOPOLYHEDROVIRUS IS A MULTIFUNCTIONAL VIRAL CYCLIN

Two major characteristics of baculovirus infection are arrest of the h ost cell at G(2)/M phase of the cell cycle with continuing viral DNA r eplication, We show that Autographa californica nucleopolyhedrovirus ( AcMNPV) encodes for a multifunctional cyclin that may partially explai n the molecular basis of these important characteristics of AcMNPV (ba culovirus) infection. Amino acids 80-110 of the viral structural prote in ODV-EC27 (-EC27) demonstrate 25-30% similarity with cellular cyclin s within the cyclin box. Immunoprecipitation results using antibodies to -EC27 show that -EC27 can associate with either cdc2 or cdk6 result ing in active kinase complexes that can phosphorylate histone H1 and r etinoblastoma protein in vitro, The cdk6-EC27 complex also associates with proliferating cell nuclear antigen (PCNA) and we demonstrate that PCNA is a structural protein of both the budded virus and the occlusi on-derived virus. These results suggest that -EC27 can function as a m ultifunctional cyclin: when associated with cdc2, it exhibits cyclin B -like activity; when associated with cdk6, the complex possesses cycli n D-like activity and binds PCNA, The possible roles of such a multifu nctional cyclin during the life cycle of baculovirus are discussed, al ong with potential implications relative to the expression of function ally authentic recombinant proteins by using baculovirus-infected cell s.