IDENTIFICATION AND CHARACTERIZATION OF A NOVEL PRFA-REGULATED GENE INLISTERIA-MONOCYTOGENES WHOSE PRODUCT, IRPA, IS HIGHLY HOMOLOGOUS TO INTERNALIN PROTEINS, WHICH CONTAIN LEUCINE-RICH REPEATS

The expression of all virulence factors in Listeria monocytogenes char acterized to date is controlled by the virulence regulator protein, Pr fA, To identify further PrfA-regulated proteins, we examined supernata nts of L. monocytogenes EGD harboring additional copies of the PrfA re gulator for the presence of novel proteins, This led to the identifica tion and biochemical purification of a hitherto uncharacterized PrfA-d ependent 30-kDa protein (A, Lingnau, T, Chakraborty, K, Niebuhr, E, Do mann, and J, Wehland, Infect. Immun. 64:1002-1006, 1996), Oligonucleot ide primers derived from internal peptide sequences of this protein al lowed the cloning and determination of the entire sequence of the resp ective gene, The protein comprised 297 amino acids with strong overall homology to the internalins, InlA and InlB, particularly in the regio n harboring the leucine-rich repeats, The gene has been designated irp A for internalin-related protein A gene, Transcriptional studies revea led that the gene was monocistronic and, like the inlA and inlB genes, was transcribed by PrfA-dependent and PrfA-independent mechanisms, Mo noclonal antibodies raised against IrpA indicated that it was produced by L. monocytogenes but not by the nonpathogenic species Listeria inn ocua, To examine the role of IrpA in pathogenesis, we constructed an i sogenic in-frame deletion mutant that removed all but 116 amino acids of the IrpA protein, This mutant was neither defective for invasion in to many tissue culture cell lines nor did it demonstrate reduced intra cellular survival, However, in vivo studies using the mouse infection model revealed that the irpA mutant showed reduced virulence compared to the parental strain, These results suggest a role for IrpA during d isseminated infection by L, monocytogenes.