Single strand binding protein specific for the polyoma early-coding strand of PEA1 (AP1) regulatory sequence.

We have shown that nuclear and cytosolic proteins from embryonal carcinoma F9 cells are able to bind to the early-coding strand of polyoma enhancer A domain. As demonstrated by mobility shift specific competition experiments, DNase I footprinting, depurination and depyrimidation interference, and proteolytic clipping performed with single stranded oligonucleotides, some of these proteins bind specifically to the early-coding PEA1 (AP1) motif. In addition, 'Southwestern' analysis has made possible the identification of a 46 KD nuclear protein that binds to this sequence. These cellular proteins did not bind to the complementary single strand as demonstrated by mobility shift analysis, nor did they bind to RNA synthesized in vitro by using the complementary strand as template. They were also shown to be different from their corresponding double strand binding factors. This new dimension in the functional flexibility and complexity of the polyoma enhancer suggests new properties of the classic regulating sequences that could provide additional modulation of regulating activities.