FACTORS REGULATING BACULOVIRUS LATE AND VERY LATE GENE-EXPRESSION IN TRANSIENT-EXPRESSION ASSAYS

Eighteen genes of Autographa californica nuclear polyhedrosis virus ar e necessary and sufficient to transactivate expression from the late v p39 promoter in transient-expression assays in SF-21 cells. These 18 g enes, known as late expression factor genes (lefs), are also required to transactivate the very late promoter of the polyhedrin gene, polh, but expression from this promoter is relatively weak compared with exp ression from the vp39 promoter. To further define the factors required for late and very late promoter expression, we first determined that the eighteen lefs were also required for expression from two other maj or baculovirus promoters: the late basic 6.9-kDa protein gene, p6.9, a nd the very late 10-kDa protein gene, p10. We next examined the effect of the very late expression factor 1 gene (vlf-1), a gene previously identified by analysis of a temperature-sensitive mutant, in the trans ient-expression assay and found that vlf-1 specifically transactivated the two very late promoters but not the two late promoters. We then s urveyed the Autographa californica nuclear polyhedrosis virus genome f or additional genes which might specifically regulate very late gene e xpression; no additional vlf genes were detected, suggesting that VLF- 1 is the primary regulator of very late gene expression. Finally, me f ound that the relative contribution of the antiapoptosis gene p35, whi ch behaves as a lef in these transient-expression assays, depended on the nature of the other viral genes provided in the cotransfection mix tures, suggesting that other viral genes also contribute to the abilit y of the virus to block apoptosis.