Disruption of type III secretion in Salmonella enterica serovar Typhimurium by external guide sequences.

The type III secretion system involved in Salmonella enterica serovar Typhimurium invasion of host cells has been disrupted using inducibly expressed oligonucleotide external guide sequences (EGSs) complementary to invB or invC mRNA. These EGSs direct single site cleavage in these mRNAs by endogenous RNase P, and their expression in Salmonella results in invC mRNA and InvC protein depletion, decreased type III secretion and interference with host cell invasion. Comparison of these effects with those from studies of Salmonella invB and invC mutants suggests that invB EGSs have polar effects on invC mRNA.