Functional analysis of the regulatory region of polyoma mutant F9-1 DNA.

Functional analysis of the transcriptional control region of the polyoma (Py) mutant F9-1 reveals that the mutation is located in a region of Py DNA required for at least two functions. First, an enhancer element which includes the F9-1 mutation was characterized by deletion analysis. This element, described previously as enhancer B is essential for viral early gene expression in F9 stem cells whereas enhancer A is unnecessary for transcriptional activity in embryonal carcinoma (EC) cells. Second, a CCACCC motif, present twice in the 3' part of enhancer B is also required in cis for the response to a heterologous enhancer. This suggests that a promoter element is present in this region of the polyoma genome which overlaps Py enhancer B. We also demonstrate the enhancement of the polyoma early promoter activity in F9 stem cells by MSV sequences. The significance of these observations is discussed.