Stimulation of simian virus 40 late gene expression by simian virus 40 tumor antigen.

Abstract

The early SV40 gene product, large tumor (T) antigen, is responsible for the initiation of viral DNA replication and the autoregulation of early gene expression through direct protein-DNA interactions. The role of T antigen in late viral gene expression, independent of its function in amplifying templates through DNA replication, was studied. SV40 DNA was transfected into African green monkey kidney BSC-1 and COS-1 cells and cultured in the presence of inhibitors of DNA replication. Electrophoretic immunoblot analysis indicated that both the onset and the extent of SV40 late gene expression is increased in COS-1 cells, which constitutively express SV40 T antigen. Blot hybridization analysis of poly(A)-selected RNA demonstrated that the level of synthesis of the major late structural protein VP-1 in COS-1 cells was due to increased transcription. Similar results were obtained when plasmids that contain the SV40 late gene but lack both the origin for viral DNA replication and the early coding region were transfected onto COS-1 cells. Using lines of SV40-transformed monkey kidney cells that express altered T antigens, enhanced expression of the late gene product was found to be correlated with the ability of T antigen to bind SV40 DNA. Evidently, large T antigen plays a role in the stimulation of late viral gene expression.