A fourth metalloprotease gene in Erwinia chrysanthemi

Erwinia chrysanthemi, a Gram-negative phytopathogenic bacterium, was previously shown to secrete 3 related extracellular metalloproteases, A, B and C via a specific signal-peptide-independent pathway. A new gene (prtG) encoding a fourth, 52-kDa metalloprotease was identified on the same recombinant cosmid (pEW1) that carries the genes for the previously described proteases (prtA, prtB and prtC), for the specific secretion factors (prtD, prtE and prtF) and for a protease inhibitor (inh) cloned from E. chrysanthemi B374. The predicted sequence of PrtG was similar to those of PrtA, PrtB and PrtC, its secretion required PrtD, PrtE and PrtF; its secretion signal was located at the C terminus but its proteolytic activity was distinct from that of the 3 other proteases. Results presented here suggest that prtG could be the first gene of an operon that includes inh, prtD, prtE and prtF.