Roles of LcrG and LcrV during type III targeting of effector Yops by Yersinia enterocolitica

Yersinia enterocolitica target effector Yop proteins into the cytosol of eu karyotic cells by a mechanism requiring the type III machinery. LcrG and Lc rV have been suggested to fulfill essential functions during the type In ta rgeting of effector Yops. It is reported here that knockout mutations of lc rG caused mutant yersiniae to prematurely secrete Yops into the extracellul ar medium without abolishing the type III targeting mechanism (Los phenotyp e [loss of type III targeting specificity]). Knockout mutations In lcrV red uced type III targeting of mutant yersiniae but did not promote secretion i nto the extracellular medium (Not [no type III targeting]), However, knocko ut mutations in both genes caused Delta lcrGV yersiniae to display a Los ph enotype similar to that of strains carrying knockout mutations in lcrG alon e. LcrG binding to LcrV resulted in the formation of soluble LcrGV complexe s in the bacterial cytoplasm. Membrane-associated, bacterial-surface-displa y ed or -secreted LcrG could not be detected. Most of LcrV was located in t he bacterial cytoplasm; however, small amounts were secreted into the extra cellular medium. These data support a model whereby LcrG may act as a negat ive regulator of type III targeting in the bacterial cytoplasm, an activity that is modulated by LcrG binding to LcrV. No support could be gathered fo r the hypothesis whereby LcrG and LcrV may act as a bacterial surface recep tor for host cells, allowing effector Yop translocation across the eukaryot ic plasma membrane.