Regulation of proline utilization in Salmonella typhimurium: characterization of put::Mu d(Ap, lac) operon fusions

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Abstract
The genes for proline utilization were fused to the structural genes of the lac operon by use of the hybrid Mu phage derivative Mu d(Aplac). Stable deletion derivatives of these fusions were selected and used to study the transcriptional regulation of the put genes. Analysis of these fusions showed that the putA gene product, a bifunctional oxidase-dehydrogenase, also serves to negatively control transcription of the putA and putP gens. Transcription of the put genes is repressed only in putA+ strains; this repression is lifted when exogenous proline is supplied. Transcription of the put genes is stimulated by cAMP in putA+ and putA strains. Maximal induction of the put genes in putA+ strains requires O2 or an alternative electron acceptor. This O2 effect is mediated by the putA protein, since putA mutants show maximal transcrption even without an electron acceptor. The orientation of the Mu d(Ap lac) insertions was determined by formation of Hfr via the lac homology on F''Ts114 lac+. The direction of chromosome mobilization by these Mu d(Ap lac)-directed Hfr demonstrated that the putP and putA genes are divergently transcribed from a central regulatory region lying between them.