c-ets-1 DNA binding to the PEA3 motif is differentially inhibited by all the mutations found in v-ets

The proto-oncogene c-ets-1, one of the two cellular sequences transduced by the avian retrovirus E26, encodes for two transcription factors that activate through a purine-rich motif. The v-ets oncogene differs from its cellular progenitor p68c-ets-1 (i) by its fusion to gag- and myb-derived sequences in the E26 P135gag-myb-ets fusion protein, (ii) by two point mutations, and (iii) by the replacement of the 13 C-terminal amino acids present in c-ets-1 by 16 unrelated residues in v-ets. A 35 kDa protein which binds to the purine-rich PEA3 motif in a sequence-specific manner has been obtained by expression in Escherichia coli of the 311 carboxy-terminal amino acids of c-ets-1. Using various v-/c-ets-1 chimeric 35 kDa proteins expressed in bacteria, we have shown that all the mutations found in v-ets, when introduced into this c-ets-1 protein, diminish or even abolish its sequence-specific DNA binding. These results demonstrate that, in addition to the previously defined 85 amino acids located near the carboxy terminus of the c-ets-1 protein (the ETS domain), other sequences are required for sequence-specific DNA binding. In addition, the c-ets-1 35 kDa polypeptide carrying the two point mutations and the viral-specific carboxy terminus, and thus similar to the v-ets-encoded domain of the E26 P135gag-myb-ets, does not bind to the PEA3 motif.