Multiple regulatory circuits for transcription from the polyhedrin gene promoter of the Autographa californica multiple nucleocapsid nuclear polyhedrosis virus

Abstract

The baculovirus expression vector system has emerged as the system of choice for the expression of a number of heterologous genes of both prokaryotic and eukaryotic origin. This system utilizes the Autographa californica multiple nucleocapsid nuclear polyhedrosis virus (AcMNPV) very late hyperactive polyhedrin gene (polh) promoter to drive the transcription of foreign genes. The transcription program of the virus is divided into a pre-replicative stage (early) and a post-replicative stage (late and very late) and occurs in a coordinately regulated and highly ordered cascade. In the very late phase, there is hyper-expression of the polh and p10 genes. Late and very late genes are under the control of an α-amanitin and tagetitoxin-resistant RNA polymerase that is induced during infection of the insect host. Despite the immense popularity of the baculovirus expression system, little is known about mechanisms of basal and hyperactivated transcription from the polh promoter. This review aims at summarizing the recent developments in understanding the cis and trans acting elements involved in transcriptional regulation from the polh promoter with particular emphasis on the role of insect cell host factors.