The gene encoding V antigen from Yersinia pestis was cloned into the plasmid expression vector pGEX-5X-2. When electroporated into Escherichia coli JM109, the recombinant expressed V antigen as a stable fusion protein with glutathione S-transferase. The glutathione S-transferase-V fusion protein was isolated from recombinant E. coli and cleaved with factor Xa to yield purified V antigen as a stable product. Recombinant V antigen was inoculated intraperitoneally into mice and shown to induce a protective immune response against a subcutaneous challenge with 3.74 x 10(6) CFU of virulent Y. pestis. Protection correlated with the induction of a high titer of serum antibodies and a T-cell response specific for recombinant V antigen. These results indicate that V antigen should be a major component of an improved vaccine for plague.