%0 Journal Article %A Liao, Min-Ken %A Gort, Steve %A Maloy, Stanley %T A cryptic proline permease in Salmonella typhimurium %D 1997 %J Microbiology, %V 143 %N 9 %P 2903-2911 %@ 1465-2080 %R https://doi.org/10.1099/00221287-143-9-2903 %K multicopy suppression %K Salmonella typhimurium %K cryptic gene %K proline transport %I Microbiology Society, %X Summary: 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 clone 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. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-143-9-2903