ACTA IS A DIMER

ActA, a surface protein of Listeria monocytogenes, is able to induce c ontinuous actin polymerization at the rear of the bacterium, in the cy tosol of the infected cells, Its N-terminal domain is sufficient to in duce actin tail formation and movement, Here, we demonstrate, using th e yeast two-hybrid system, that the N-terminal domain of ActA may form homodimers. By using chemical cross-linking to explore the possibilit y that ActA could be a multimer on the surface of the bacteria, we sho w that ActA is a dimer, Cross-linking experiments on various L. monocy togenes strains expressing different ActA variants demonstrated that t he region spanning amino acids 97-126, and previously identified as cr itical for actin tail formation, is also critical for dimer formation, A model of actin polymerization by L. monocytogenes, involving the Ac tA dimer, is presented.