Elk-1 and SRF form a ternary complex on DNA. (A) EMSA using a 32P-labeled vSRE probe (lane 1) in the presence of recombinant SRF (rSRF) (lane 2), recombinant Elk-1 (rElk-1) (lane 3), or rElk-1 and rSRF (lanes 4 to 7). Specific antibody to Elk-1 (lane 5), SRF (lane 6), or AP-2 (lane 7) was added in the indicated reactions. The locations of supershifted bands are indicated on the right. (B) EMSA using 32P-labeled vSRE probe (lane 1) incubated with CEM nuclear extracts (lanes 2 to 5). Antibodies were added to the indicated lanes. The positions and identities of supershifted bands are indicated on the right. (C) EMSA using a vSRE probe (lane 1) incubated with CEM nuclear extracts (lanes 2 to 4) and a 25-fold excess of unlabeled vSRE (lane 3) or mvSRE (lane 4) used as specific or nonspecific competitors, respectively. Wild-type vSRE competes for the Elk-1 band (arrow). (D and E) Western blots of SRF and Elk-1 using recombinant proteins (D) or whole cell extracts (E) from MS9, 293, or CEM cells.