IDENTIFICATION OF 4 NEW MEMBERS OF THE INTERNALIN MULTIGENE FAMILY OFLISTERIA-MONOCYTOGENES EGD

Listeria monocytogenes is a bacterial pathogen that is able to invade nonphagocytic cells. Two surface proteins, internalin, the inlA gene p roduct, and InlB, play important roles in the entry into cultured mamm alian cells. These proteins also have extensive sequence similarities. Previously, Southern hybridization predicted the existence of an inte rnalin multigene family. Recently, InlC, a secreted protein of 30 kDa homologous to InlA and InlB,,vas identified. In this work, we identifi ed and characterized four new members of the internalin multigene fami ly, inlC2, inlD, inlE, and inlF which encode proteins of 548, 567, 499 , and 821 amino acids respectively, inlC2, inlD, and inlE are contiguo us on the chromosome of L. monocytogenes EGD, whereas inlF is located in a different chromosomal region, These four inl gene products displa y the principal features of internalin, namely, a signal sequence, two regions of repeats (or LRR and B repeats), and a putative cell wall a nchor sequence containing the sorting motif LPXTG, The four inl genes were maximally expressed albeit at a low level during early exponentia l growth in bacterial medium at 37 degrees C, The role of these inl ge nes in L. monocytogenes invasion was assessed by constructing isogenic chromosomal deletion mutants and testing them for entry into various nonphagocytic cells. Unexpectedly, the inlC2, inlD, inlE, and inlF nul l mutants were not affected for entry into any of the cell lines teste d, raising the possibility that these genes are needed for an aspect o f pathogenicity other than invasion, The identity of such an aspect re mains to be determined.