SUMMARY: In , the synthesis of histidase, urocanase and amidase is severely repressed when succinate is added to a culture growing in pyruvate + ammonium salts medium. When growth is nitrogen-limited, catabolite repression by succinate of histidase and urocanase synthesis does not occur but succinate repression of amidase synthesis persists. Amidase synthesis is not regulated in the same way as histidase synthesis by the availability of other nitrogen compounds for growth.

Growth of strain PACI in succinate+histidine media is nitrogen-limited since this strain is defective in a histidine transport system. When methyl-ammonium chloride is added to succinate+histidine media, growth inhibition occurs. Mutants isolated from succinate+-histidine + methylammonium chloride plates were found to be resistant to catabolite repression by succinate even in ammonium salts media. It is suggested that the genes of may be regulated in the same way as in , by induction by urocanate and activation by either the cyclic AMP-dependent activator protein or by glutamine synthetase.


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