title: A cryptic proline permease in Salmonella typhimurium.
abstract: Wild-type Salmonella typhimurium expresses three proline transport systems: a high-affinity proline transport system encoded by the putP gene, and two glycine betaine transport systems with a lower affinity for proline encoded by the proP and proU genes. Although proline uptake by the ProP and ProU transport systems is sufficient to supplement a proline auxotroph, it is not efficient enough to allow proline utilization as a sole source of carbon or nitrogen. Thus, the PutP transport system is required for utilization of proline as a carbon or nitrogen source. In this study, an overexpression suppressor, designated proY, which allows proline utilization in a putP genetic background and does not require the function of any of the known proline transport systems, was cloned and characterized. The suppressor gene, designated proY, maps at 8 min on the S. typhimurium linkage map, distant from any of the other characterized proline transport genes. The DNA sequence of the proY gene predicts that it encodes a hydrophobic integral membrane protein, with strong similarity to a family of amino acid transporters. The suppressor phenotype requires either a multicopy done of the proY+ gene or both a single copy of the proY+ gene and a proZ mutation. These results indicate that the proY gene is the structural gene for a cryptic proline transporter that is silent unless overexpressed on a multicopy plasmid or activated by a proZ mutation.
authors.affiliation: Department of Microbiology, University of Illinois, B103 Chemical and Life Sciences Laboratory, 601 S. Goodwin Ave, Urbana, IL 61801, USA.
authors.forename: Min-Ken
authors.initials: MK
authors.lastname: Liao
authors.affiliation: Department of Microbiology, University of Illinois, B103 Chemical and Life Sciences Laboratory, 601 S. Goodwin Ave, Urbana, IL 61801, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Gort
authors.affiliation: Department of Microbiology, University of Illinois, B103 Chemical and Life Sciences Laboratory, 601 S. Goodwin Ave, Urbana, IL 61801, USA.
authors.forename: Stanley
authors.initials: S
authors.lastname: Maloy
mesh_terms: D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001693:Biological Transport, Active / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D016153:Genes, Suppressor; D008040:Genetic Linkage; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D011392:Proline / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; D000597:Amino Acids, Branched-Chain; D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; C060774:ProU protein, Bacteria; C033082:proline transporter; D011392:Proline