Enhancement of RNA polymerase III transcription by the E1A gene product of adenovirus.

Nuclear extracts from adenovirus-infected HeLa cells harvested early in infection demonstrated a markedly increased capacity for transcription by RNA polymerase III of exogenous VA RNA genes, as well as cloned tRNA and 5S RNA genes. In contrast, no enhanced transcription was observed in extracts from cells infected with an E1A deletion mutant. Moreover, cells co-transfected with the VA- and E1A-containing plasmids showed markedly higher levels of VA RNA synthesis than did cells transfected with the VA-containing plasmid alone. Although analysis of high ionic strength extracts revealed that the enhancement of pol III transcription persists late in infection, moderate ionic strength extracts indicated that transcription factor IIIC becomes limiting. Chromatographic fractionation and complementation analysis of extracts from mock- and virus-infected cells indicated that the factor(s) responsible for the enhanced activity was localized entirely in the fraction containing transcription factor IIIC.