RT Journal Article SR Electronic(1) A1 Edwards, R. M. A1 Yudkin, M. D.YR 1984 T1 Tryptophanase Synthesis in Escherichia coli: the Role of Indole Replacement in Supplying Tryptophan and the Nature of the Constitutive Mutation tnaR3 JF Microbiology, VO 130 IS 6 SP 1535 OP 1542 DO https://doi.org/10.1099/00221287-130-6-1535 PB Microbiology Society, SN 1465-2080, AB The properties of the tryptophanase constitutive mutation tnaR3 have been investigated. It has previously been reported that mutants carrying tnaR3 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 tnaR3 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 tnaR3 is cis-dominant, but no evidence was found for any effect in trans. In addition to rendering tryptophanase synthesis constitutive, tnaR3 affects the response of tryptophanase synthesis to different growth temperatures., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-130-6-1535