AlcS is a predicted MFS transporter encoded within the Bordetella alcaligin siderophore gene cluster. (A) Molecular structure of alcaligin siderophore [1,8(S),11,18(S)-tetrahydroxy-1,6,11,16-tetraazacycloeicosane-2,5,12,15-tetrone] produced by Bordetella species. (B) Spatial organization of the Bordetella alcaligin siderophore gene cluster. The linear genetic map represents an approximately 12-kb BamHI-PstI chromosomal DNA region of B. bronchiseptica and B. pertussis (41). The arrows indicate the transcriptional orientations of genes, and the open rectangles upstream from alcA, alcR, and fauA represent the locations of known Fur-regulated promoter-operator regions. The arrow representing the alcS gene is shaded. (C) Multiple-protein sequence alignment of AlcS with representative bacterial MFS transporters with known functions. The proteins and GenBank accession numbers are as follows: AlcS, the Bordetella alcaligin exporter protein (B. bronchiseptica accession no. NP_890434, B. pertussis accession no. NP_881089); E. coli Bcr bicyclomycin resistance protein (accession no. P28246); Pseudomonas aeruginosa chloramphenicol resistance protein CmlA (accession no. P32482); E. coli multidrug resistance protein EmrD (accession no. P31442); and E. coli multidrug resistance protein MdfA (accession no. CAA69997). In the ClustalW alignment consensussequence, asterisks indicate residues that are identical in all sequences, colons indicate conserved substitutions, and periods indicate semiconserved substitutions. Predicted transmembrane segments of AlcS are overlined, and motif A conserved among 12-transmembrane segment MFS proteins is shaded.