Genetic organization of the RTX gene cluster ( tolC-rtxA1-rtxD-rtxB ) in L. hongkongensis. The boxes represent the CDSs. The number of amino acid residues of each gene is indicated above the boxes. The basic functional activities of the corresponding gene products are given on the top. Five copies of glycine-rich nonapeptide repeats (GGXGXDX[L/I/V/W/Y/F]X, where X is any amino acid) of rtxA1 are underlined. An CDS of unknown function, located between rtxA1 and rtxD, are also depicted, where nine repeats of 22 amino acids are highlighted. The relative positions of each gene are assigned as predicted by nucleotide sequence analysis.