In vitro transactivation of baculovirus early genes by nuclear extracts from Autographa californica nuclear polyhedrosis virus-infected Spodoptera frugiperda cells

Abstract

Nuclear extracts, prepared from Autographa californica nuclear polyhedrosis virus-infected Spodoptera frugiperda cells during a time course of infection, were analyzed for activation of early gene transcription and for late gene transcription. The templates used in the in vitro transcription assays contained promoters for baculovirus genes that have been classified as immediate early, delayed early, and late. The promoters were derived from the baculovirus 39K, p26, gp64, and DNA polymerase genes. In addition, the adenovirus major late promoter was included in these studies. We found that transcription from promoters classified as immediate early or delayed early was accurately initiated by using extracts from uninfected cells. Furthermore, transcription from all early promoters tested was found to be transactivated by nuclear extracts prepared at 4 and 8 h postinfection. However, baculovirus enhancer-dependent transcriptional activation was not observed in tests with templates containing the hr5 enhancer sequence. Transcription from baculovirus late promoters was also not observed. A decline in transcription by nuclear extracts prepared from cells late in infection was associated with the presence of DNase activity.