Actin distribution is disrupted upon expression of Yersinia YopO/YpkA in yeast.

Pathogenic Yersinia spp. use a Type III secretion system to inject effector proteins directly into host cells. The effector proteins interfere with normal cellular signalling and disrupt cytoskeletal structures that are required for phagocytosis of the invader. Here we show that Saccharomyces cerevisiae responds to one of these effector proteins, YopO/YpkA, essentially as has been observed in mammalian model systems. Expression of YopO in yeast results in inhibition of growth on solid medium. YopO expression confers a cytotoxic effect upon yeast with only 6% of cells remaining viable after 3 h of expression. Moreover, there is no obvious cell cycle arrest associated with cytotoxicity. YopO expression disrupts the normal distribution of actin in yeast. Actin is no longer observed exclusively at sites of cell growth. Concurrent with disruption of actin, we find YopO localizes to the cell periphery, where it may disrupt actin localization. Inactivation of the YopO kinase has no apparent effect upon the deleterious effects of YopO. Collectively, our results show that the yeast model system that has been constructed meets all requirements to serve as an excellent genetic model to exploit examination of YopO and its intracellular targets. Copyright 2004 John Wiley & Sons, Ltd.