Two genes are involved in the degradation of proline to glutamic acid. The putP gene encodes a proline permease; the putA gene encodes a bifunctional degradative enzyme. Although the two genes are transcribed independently, both genes are induced by exogenous proline and are subject to catabolite repression. The putA gene product appears to function also as an autogenous repressor protein acting on both the putA and putP transcription units. Regulatory mutations map throughout the putA gene; these are correctable by an episomal putA+ gene, which acts in trans to restore repression.
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