MUTATIONAL ANALYSIS OF A BACULOVIRUS MAJOR LATE PROMOTER

We have used a linker-scan mutation strategy to analyze P(cap99), the proximal promoter of the Autographa californica nuclear polyhedrosis v irus (AcMNPV) gene encoding the major capsid protein. A series of reco mbinant viruses expressing the cat reporter gene under the control of selected mutants of this promoter was constructed. Only mutations that altered bases within a region extending from 8 bp upstream to 6 bp do wnstream from a TAAG sequence had a significant effect on expression f rom the late gene promoter. A synthetic promoter consisting of only th ese 18 bp (P(capmin)) was sufficient to direct late expression. Aside from this small region surrounding the TAAG, no evidence for distinct late activating or repressing sequence elements was obtained. Experime nts comparing and combining late and very late gene promoter sequences suggest that late expression is intrinsically determined by the prese nce and immediate context of a TAAG sequence and that very late expres sion [as previously shown in Ooi et al., J. Mol. Biol. 210 (1989) 721- 736] results from additional modulation of TAAG-dependent expression b y downstream promoter elements placed in an appropriate context. A com pact combination promoter (95 bp), constructed by fusing P(capmin) to a linker-modified very tate polyhedrin promoter, directs strong expres sion at late and very late times post-infection.