Baculovirus late and very late gene regulation.

Baculoviruses have adapted novel tactics to transcribe their genes during the late stages of replication. These include a DNA-directed RNA polymerase which is evolutionarily divergent from cellular polymerases. The viral RNA polymerase is a multisubunit and multifunctional RNA polymerase that has the ability to recognize late promoters, transcribe the linked genes, and process the transcripts at both 5' and 3' ends. The viral RNA polymerase binds to late viral gene promoter elements that are compact and differ from early viral gene and cellular promoters. Baculoviruses also encode a number of proteins devoted to the synthesis of late transcripts. Many of these are highly conserved among all the baculovirus genomes sequenced to date, suggesting common transcription mechanisms. Although viral late mRNAs resemble host mRNAs, the transcribing/processing machinery is distinct. Characterization of the late gene transcription apparatus will elucidate new viral mechanisms for transcription.