ELK-1 CAN RECRUIT SRF TO FORM A TERNARY COMPLEX UPON THE SERUM RESPONSE ELEMENT

The initial genomic response to serum growth factors is the transcript ional activation of a set of immediate-early genes, Serum-induced tran scriptional activation of several of these genes involves the formatio n of a ternary complex that includes the serum response factor (SRF), a 62 kDa ternary complex factor (TCF) and a serum response element (SR E), TCF alone does not bind the SRE of the protooncogene c-fos, but re quires the prior assembly of the SRF-SRE binary complex for it to be r ecruited into a ternary complex, Here we show that this SRF-SRE binary complex is not an obligatory prerequisite for the formation of a seru m responsive ternary complex, We demonstrate that Elk-l, which has pro perties of TCF, can recruit SRF into a ternary complex on elements tha t do not support formation of the SRF-DNA binary complex, We also show that for two immediate-early genes, pip92 and nur77, formation of the ternary complex may occur without the prior assembly of SRF-DNA binar y complex, Finally, we show that the ability of different sequences to support formation of Elk-1-SRF-DNA ternary complex in vitro correlate s with their ability to respond to serum growth factors in vivo. Our r esults suggest that a much broader range of DNA sequences than the con sensus SRF and TCF binding sites can support ternary complex formation , and by inference, serum induction, Possible implications of these re sults are discussed.