trans-activation of RNA polymerase II and III promoters by SV40 small t antigen.

A biochemical role for SV40 small t antigen (t) in the viral infectious cycle that would explain the strong conservation of t structure among papovaviruses and its role as a helper of SV40 large T antigen function in the viral transforming process is not understood. Here, we report an intracellular biochemical function of the protein--the capacity to trans-activate selected RNA polymerase II and III-requiring promoters. Since t has failed in the past to bind to DNA and did not stimulate all polymerase II-requiring promoters tested, it likely trans-activates, at least in part, by modifying the activity of selected transcription factors.