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.     

The cell-specific enhancer of the mouse transthyretin (prealbumin) gene binds a common factor at one site and a liver-specific factor(s) at two other sites.

We previously defined two distinct cell-specific DNA elements controlling the transient expression of the transthyretin gene in Hep G2 (human hepatoma) cells: a proximal promoter region (-202 base pairs [bp] to the cap site), and a far-upstream cell-specific enhancer located between 1.6 and 2.15 kilobases (kb) 5' of the cap site (R. H. Costa, E. Lai, and J. E. Darnell, Jr., Mol. Cell. Biol. 6:4697-4708, 1986). In this report, we located the effective transthyretin enhancer element within a 100-bp region between 1.96 and 1.86 kb 5' to the mRNA cap site. In Hep G2 nuclear extracts, three protein-binding sites within this minimal enhancer element were identified by gel mobility and methylation protection experiments. Each binding site was required for full enhancer activity in Hep G2 transient expression assays. Competition experiments in protein-binding assays suggested that two of the three sites were recognized by a similar factor and that the protein interaction with the third site was different. The nuclear protein(s) which bound to the two homologous sites was found mainly or only in cells of hepatic origin, suggesting an involvement of this region in the cell-specific function of this enhancer. The nuclear protein(s) recognizing the third enhancer region was also found in HeLa and spleen cells.