Interaction of nuclear factor EF-1A with the polyomavirus enhancer region.

Enhancer factor 1A (EF-1A) is a mammalian nuclear protein that previously was shown to bind cooperatively to the repeated core enhancer element I sequence in the adenovirus E1A enhancer region. We now have characterized three binding sites for EF-1A in the polyomavirus A2 (Py) enhancer region. Site 1 resides in the Py A enhancer domain, and sites 2 and 3 reside in the Py B enhancer domain. EF-1A binding to Py site 1 is independent of cooperation with other EF-1A sites or the adjacent binding sites for PEA-1 and PEA-2, two murine nuclear factors that bind in the Py A enhancer domain. EF-1A binding to Py sites 2 and 3, in contrast, is cooperative, similar to the situation previously observed with binding sites in the adenovirus E1A enhancer region. In a transient replication assay, EF-1A site 1 functions synergistically with the PEA-1 and PEA-2 sites in the A enhancer domain to enhance Py replication. The functional cooperativity observed with the EF-1A, PEA-1, and PEA-2 sites in vivo does not reflect cooperative DNA binding interactions, as detected in vitro. Py EF-1A site 1 alone is capable of weakly stimulating Py replication. EF-1A site 1 overlaps with the binding sites for the murine nuclear protein PEA-3 and the ets family of oncoproteins.