Transcription of the tryptophan operon in polarity mutants of Escherichia coli: II. Evidence for normal production of tryp-mRNA molecules and for premature termination of transcription

摘要: Studies were performed with tryptophan-operon polarity mutants to determine whether normal numbers of tryp-mRNA molecules produced by these strains and the short detected (Imamoto & Yanofsky, 1967) resulted from selective degradation regions intact tryp-mRNA. In experiments in which pulse-labeling was immediately after shift bacterial cultures repression derepression conditions, production early observed all examined. When at different times prior appearance first wild-type strain (before six minutes initiation derepression), reduced levels polar mRNA region corresponding operon beyond nonsense codon conspicuously absent. Since growing chain is presumably attached site synthesis during this period, it seems unlikely that could be responsible for are detected. It found decreasing pulse period transcription failed increase relative amount total detectable or level genes gene mutation. addition, sucrose gradient sedimentation studies detect a profile higher molecular weight as time decreased. These findings suggest mutations may cause premature termination an vicinity introduced codon.