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Fig. 1 | BMC Microbiology

Fig. 1

From: Fratricide activity of MafB protein of N. meningitidis strain B16B6

Fig. 1

Organization of maf islands in various N. meningitidis genome sequences. Most islands contain a mafA, mafB (indicated by their locus tags) and a variable repertoire of mafB-CTs interspersed with ORFs, called mafIs, which may encode immunity proteins (indicated with open arrows). It is not clear whether all these intervenient ORFs are required to confer immunity against the toxin encoded by the upstream mafB or mafB-CT gene. Islands are classified as MGI-1, MGI-2 and MGI-3 according to [10]. The phylogenic groups of the mafA and mafB genes as defined in Fig. 2 are also indicated. The genes flanking the islands are colored green. MGI-1 contains a mafA and mafB from clusters I and is flanked by anmk coding for anhydro-N-acetylmuramic acid kinase and an ORF encoding a small peptide of 91 aa that shows high sequence similarity with the N terminus of the iron-regulated RTX toxin FrpC. MGI-2 contains a mafB of cluster II and usually also a mafA and mafB of clusters I. This island is flanked by a proline tRNA gene and trk encoding a potassium transport system. MGI-3 contains mafA and mafB genes of clusters II and III, respectively, and is flanked by genes encoding UMP kinase (pyrH) and the putative signal peptide peptidase SppA. The mafB and mafB-CT genes can share sequence identities in their central and 5’ regions, respectively (underlined), that are probably used for homologous recombination. These regions are specific for each mafB group, which is indicated by the different colors of the underlining. The 3’ end of the mafB and mafB-CT genes corresponds to the toxic domain; it is hypervariable as indicated by different colors. The mafIs remain associated with the 3’ end of the upstream mafB or mafB-CTs during genetic rearrangements in the maf islands; therefore, they are colored accordingly. Often additional intervenient ORFs are also found behind the mafIs (colored black); whether they also contribute to conferring immunity or have other functions (or no function at all) is not clear. The presence of an IS4 transposase gene in MGI-2 of strain G2136 is also indicated. Disrupted genes are indicated with red slashes. Regions that share more than 85 % of sequence similarity between two islands are indicated with grey shadows. ORFs indicated in this figure are based on genome annotations and our own analysis

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