RecA protein plays several key roles in the SOS response. We have constructed truncated proteins and examined their capacity to accomplish Weigle reactivation and mutagenesis of bacteriophage lambda and recombination in Escherichia coli. Our data indicate that the 17 carboxyl terminal amino acids are not essential to RecA function. However in the presence of wild-type RecA protein, the truncated protein reduces the efficiency of recombination without affecting either mutagenesis or induction of an SOS gene or Weigle reactivation. The data presented here suggest that activation of RecA protein does not involve mixed multimers or is not affected by their presence.