REGULATION OF SURFACE PRESENTATION OF ICSA, A SHIGELLA PROTEIN ESSENTIAL TO INTRACELLULAR MOVEMENT AND SPREAD, IS GROWTH-PHASE DEPENDENT

After lysing the phagocytic vacuole, Shigella spp. accumulate filament s of polymerized actin on their surface at one pole, leading to the fo rmation of actin tails that enable them to move through the cytoplasm. We have recently demonstrated that the Shigella protein IcsA is locat ed at the pole that is adjacent to the growing end of the actin tail ( M. B. Goldberg, O. Barzu, C. Parsot, and P. J. Sansonetti, J. Bacterio l. 175:2189-2196, 1993). Not every bacterium that is observed within t he cytoplasm has an actin tail. The factors that determine when a bact erium wilt form a tail are unknown. Here we demonstrate that at the mo ment of initiation of movement, Shigella spp. are frequently in the pr ocess of division. Furthermore, the expression of IcsA on the surface of the bacteria occurs in a growth phase-dependent fashion, suggesting that the surface expression of IcsA per se determines the observed as sociation of bacterial division with movement.