M. Mergeay

The sss gene product, which affects pyoverdin production in Pseudomonas aeruginosa 7NSK2, is a site-specific recombinase.

Pyoverdin production by Pseudomonas aeruginosa strain 7NSK2 was induced by Zn(II) in the presence of iron. A mutant was isolated in which Zn(II) no longer induced pyoverdin production. The sss gene which was inactivated in this mutant was cloned and sequenced. Its protein sequence showed 50% identity to the XerC protein of Escherichia coli, which is a member of the lambda integrase family of site‐specific recombinases. An open reading frame was found upstream of sss whose protein sequence showed strong identity to DapF, the diaminopimelate epimerase. In E. coli, xerC is part of a multicistronic unit that also contains dapF. The sss gene of P. aeruginosa could restore site‐specific recombination at cer in an E. coii xerC mutant and the E. coii xerC gene could complement a genomic sss mutation in P. aeruginosa.

Czc/Cnr efflux: a three‐component chemiosmotlc antiport pathway with a 12‐transmembrane‐helix protein

251 AcrA SLYQIDPATy AcrE SLYQIDPATY OrfA QLYQIDPATY CzcB VLAVIAST.. CnrB VLALVDSP.. SPRPFKKGSS QATYDSAKGD QANYDSAKGE EADYQSAQAN . .GLSDQRSE ..EAAGMAAE RIGGDGAKSR LAKAQAAANI LAKSEAAAAl LASTQEQA.. LLAAQKRLDL RKVAQAKADL GGCLSAQTEL AQLTVNRYQK AHLTVKRYVP QRYKL AHVTYDREKK ARKTYEHEAS AEAVLERNTR 300 LLGTQyiSKQ LVGTKYISQQ LVADQAVSKQ LWEQKISAEQ LFQQGVTPRQ LGERGAASEA Fig. 1. Partial multiple alignments of srx MFPs. The numbers are the position numbers of the compiete multiple alignment. Amino acids which are conserved in at least five of the six genes are emphasized with asterisks.