LcrG secretion is not required for blocking of Yops secretion in Yersinia pestis

Background: LcrG, a negative regulator of the Yersinia type III secretion apparatus has been shown to be primarily a cytoplasmic protein, but is secreted at least in Y. pestis. LcrG secretion has not been functionally analyzed and the relevance of LcrG secretion on LcrG function is unknown. Results: An LcrG-GAL4AD chimera, originally constructed for two-hybrid analyses to analyze LcrG protein interactions, appeared to be not secreted but the LcrG-GAL4AD chimera retained the ability to regulate Yops secretion. This result led to further investigation to determine the significance of LcrG secretion on LcrG function. Additional analyses including deletion and substitution mutations of amino acids 2-6 in the N-terminus of LcrG were constructed to analyze LcrG secretion and LcrG's ability to control secretion. Some changes to the N-terminus of LcrG were found to not affect LcrG's secretion or LcrG's secretion-controlling activity. However, substitution of poly-isoleucine in the N-terminus of LcrG did eliminate LcrG secretion but did not affect LcrG's secretion controlling activity. Conclusion: These results indicate that secretion of LcrG, while observable and T3SS mediated, is not relevant for LcrG's ability to control secretion.