The properties of the tryptophanase constitutive mutation have been investigated. It has previously been reported that mutants carrying grow poorly on medium that selects for constitutive expression of tryptophanase. Our results now show that this poor growth can be explained by the inability of tryptophanase to catalyse the synthesis of L-tryptophan from indole, pyruvate and ammonia at a rate sufficient to allow normal growth. Improved media for the characterization of tryptophanase constitutive mutants are described. The mutation rendered tryptophanase synthesis constitutive (at a differential rate that at 37 °C is 30% of the fully induced wild-type) and not further inducible. Diploid studies showed that is cis-dominant, but no evidence was found for any effect in . In addition to rendering tryptophanase synthesis constitutive, affects the response of tryptophanase synthesis to different growth temperatures.


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