Nucleotide sequence of a gene encoding the novel Yersinia enterocolitica heat-stable enterotoxin that includes a pro-region-like sequence in its mature toxin molecule.

A novel ST (Y-STc) produced by a pathogenic strain of Yersinia enterocolitica was recently purified and the mature toxin was found to include the pro-region-like sequence (Yoshino et al., FEBS Lett 362: 319-322, 1995). In the present study, we report the nucleotide sequence of the ystC gene. We also present the amino acid sequence of a ystC gene product secreted by a recombinant strain of Escherichia coli. From the nucleotide sequence of ystC gene, the Y-STc precursor protein was deduced to consist of 72 amino acid residues and to be comprised of two regions (pre- and mature toxin regions), while the known ST precursor proteins are comprised of three regions (pre-, pro-, and mature toxin regions). Therefore, we concluded that a long polypeptide corresponding to a pro-toxin of other Sts is secreted as the Y-STc mature toxin. This implies that the proteolytic processing of a pro-form appearing in the periplasm is not essential for the secretion of Yersinia-ST to the extracellular through the outer membrane. The recombinant Y-STc released by E. coli was found to be shorter and composed of C-terminal 24 amino acid residues of the native Y-STc. On the basis of these results, we propose that the cleavage site between the pro- and mature toxin regions of ST depends on both the amino acid sequence of the pro-toxin and on the bacterial protease system responsible for the maturation.