Transcription of class III genes activated by viral immediate early proteins

The adenovirus EIA and pseudorabies virus immediate early (IE) proteins induce transcription from transfected viral and nonviral genes transcribed by RNA polymerase II (class II genes). These proteins have now been shown also to activate transcription of transfected genes transcribed by RNA polymerase III (class III genes). As previously observed for class II genes, this stimulation of class III gene transcription was much greater for transfected genes than for the major endogenous cellular class III genes. Extracts made from cell lines stably expressing a transfected pseudorabies virus IE gene were 10 to 20 times more active in the in vitro transcription of exogenously added class III genes than extracts of the parental cell line. These results indicate that the E1A and IE proteins stimulate the expression of class III genes by a mechanism similar to the mechanism for stimulation of class II gene transcription by these proteins.