Characterisation of the Type III Secretion Protein YscU in Yersinia pseudotuberculosis
The YscU/FlhB protein family is very highly conserved, amino acid sequence homologies between the cytoplasmic domains being particularly high. Here we investigated a feature common to YscU and FlhB, i. e. the cleavage of the proteins within the C-terminal cytoplasmic tail. We could conclude that the cleavage is not connected to TTSS regulation. Nor is it required for YscU function in Yersinia type III secretion, since the uncleavable YscU variants are able to restore Yop secretion to a yscU null mutant strain. However, if YscU is not cleaved within the cytoplasmic tail, it has a toxic effect on the bacteria. The fact that Yersinia strains expressing the uncleavable YscU point mutant proteins are seriously inhibited for growth shows that the cleavage is required for survival of the bacterium.
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