THE UNRELATED SURFACE-PROTEINS ACTA OF LISTERIA-MONOCYTOGENES AND ICSA OF SHIGELLA-FLEXNERI ARE SUFFICIENT TO CONFER ACTIN-BASED MOTILITY ON LISTERIA-INNOCUA AND ESCHERICHIA-COLI RESPECTIVELY

Listeria monocytogenes and Shigella flexneri are two unrelated faculta tive intracellular pathogens which spread from cell to cell by using a similar mode of intracellular movement based on continuous actin asse mbly at one pole of the bacterium, This process requires the asymmetri cal expression of the ActA surface protein in L. monocytogenes and the IcsA (VirG) surface protein in S. flexneri, ActA and IcsA share no se quence homology. To assess the role of the two proteins in the generat ion of actin-based movement, we expressed them in the genetic context of two nonactin polymerizing, non-pathogenic bacterial species, Lister ia innocua and Escherichia coli, In the absence of any additional bact erial pathogenicity determinants, both proteins induced actin assembly and propulsion of the bacteria in cytoplasmic extracts from Xenopus e ggs, as visualized by the formation of characteristic actin comet tail s. E. coli expressing IcsA moved about two times faster than Listeria and displayed longer actin tails, However, actin dynamics (actin filam ent distribution and filament half-lives) were similar in IcsA- and Ac tA-induced actin tails suggesting that by using unrelated surface mole cules, L. monocytogenes and S. flexneri move intracellularly by intera cting with the same host cytoskeleton components or by interfering wit h the same host cell signal transduction pathway.