Effect of dnaA and rpoB mutations on attenuation in the trp operon of Escherichia coli

Abstract

The rate of synthesis of tryptophan synthetase was found to be increased by heat inactivation of the dnaA protein in three dnaA mutants temperature sensitive for initiation of DNA replication. The effect of the dnaA mutations was dependent upon the presence of an intact attenuator in the tryptophan operon. The activity of the mutated dnaA protein at the tryptophan attenuator and its activity as initiator for chromosome replication decreased gradually with increasing temperature. Two rpoB mutations that suppress the temperature defect of the dnaA46 mutation in initiation of replication were tested for effects on attenuation in the tryptophan operon. One of the rpoB mutations caused increased transcription termination at the attenuator independent of the dnaA allele, whereas the other mutation had no effect. Expression of the histidine and threonine operons, which are also regulated by attenuation, was unaffected by the dnaA mutations. the aromatic amino acids per ml, 100 ,ug of serine, leucine, and arginine per ml, and 50 pg of the other amino acids, except cysteine, per ml. In some experiments tyrosine or histidine was omitted depending on the enzyme assays to be carried out in addition to the measurements of tryptophan synthetase (TSase).Preparation of P1 lysates and Pl transductions were carried out as described by Miller (27). Deo+ transductants were selected on AB minimal plates supplemented with 0.2% thymidine as the carbon source, and Tna+ transductants were selected on 985 on August 2, 2020 by guest

The distribution and properties of RNA primed initiation sites of DNA synthesis at the replication origin ofEscherichia colichromosome

“…The transcription termination sites inside the oriC do not coincide with the major r-strand transition sites we have detected in this work, but locate closer to the core dnaA-protein binding sites (5,6). It has been suggested that dnaA gene products interact physically with RNA polymerase (39) and act in the attenuation of transcription of tryptophane operon (40). Unfortunately, we could not find a change in the level of the transcripts which were terminated at these sites upon the temperature inactivation of dnaA-gene products in vivo (our unpublished result).…”