The maturation of the 33-kDa proenzyme to the 29-kDa phosphatidylcholine phospholipase C (PC-PLC) of Listeria monocytogenes requires the production of the zinc metalloprotease encoded by mpl, the proximal gene of the lecithinase operon. We recently described a low-virulence lecithinase-deficient mutant of L. monocytogenes EGD-SmR, designated JL762, generated by a single insertion of transposon Tn1545 in mpl. This mutant failed to produce the 29-kDa PC-PLC, an exoenzyme probably involved in cell-to-cell spreading. The role of the product of the mpl gene in production of PC-PLC was investigated in trans-complementation experiments. The entire mpl gene was cloned in a plasmid able to replicate in L. monocytogenes. This recombinant plasmid was introduced into JL762 and restored the lecithinase phenotype on egg yolk agar and the production of the active 29-kDa PC-PLC in culture supernatants and partially restored the level of virulence. These results demonstrate that zinc-dependent metalloprotease of L. monocytogenes is involved in the virulence of this bacteria at least through its action on PC-PLC
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