When a growing culture of a tryptophan auxotroph of Escherichia coli is transferred to a tryptophan-free medium, the bacteria exhaust their supply of Trp-transfer ribonucleic acid (tRNA). Under these conditions transcription of the trp operon is derepressed. When l-tryptophan, dl-4-methyltrytophan, dl-6-methyltryptophan, or dl-7-azatryptophan is added to a tryptophan-starved culture, charging to tRNA(Trp) can be detected with each of these compounds except 6-methyltryptophan. Under these conditions, transcription initiations on the trp operon are repressed completely by tryptophan, 4-methyltryptophan, and 6-methyltryptophan, but only slightly by 7-azatryptophan. If a culture of a bacterium containing an altered tryptophanyl-tRNA synthetase (trpS(-)) is starved for tryptophan in the same manner, tRNA(Trp) is uncharged, but transcription of the operon is derepressed to only about one-third the level observed in trpS(+) cultures. When tryptophan, 4-methyltryptophan, 6-methyltryptophan, or 7-azatryptophan is added to a tryptophan-starved trpS(-) culture, tRNA(Trp) is charged with tryptophan but apparently not with the analogues. However, tryptophan, 4-methyltryptophan, and 6-methyltryptophan completely repress transcription initiations, whereas 7-azatryptophan derepresses transcription initiations to approximately the level of partial repression observed in trpS(+) cultures in the presence of 7-azatryptophan. When tryptophan is added to a tryptophan-starved trpS10110 culture, there is a 2-min delay before tRNA(Trp) appears to be charged. However, under these conditions, transcription initiations on the trp operon are repressed immediately by the addition of tryptophan. We interpret these results as indicating that Trp-tRNA is not the corepressor of the trp operon.

Bacterial Proteins↗

PubMed1971

Influence of chromosome structure on the frequency of tonB trp deletions in Escherichia coli.

The frequency of tonB trp deletions varies in different strains and substrains of Escherichia coli. Studies with chromosomal hybrids constructed by transducing various segments of the cysB-trp-suIII region from K-12(Ymel) into K-12(W3110) indicate that the characteristic low deletion frequency of K-12(Ymel) is determined largely by the (genetic) structure of the trp-suIII region of the chromosome. Transduction of the trp region from K-12(W3110) or K-12(Ymel) into strain B has little effect on the frequency of tonB trp deletions in that strain. When tonB trp deletions occur at 42 C rather than at 37 C, there is a significant reduction in the frequency of deletions in all strains examined except K-12(Ymel) and hybrids exhibiting a Ymel deletion pattern. The magnitude of this temperature effect in different K-12 strains increases proportionally with the frequency of tonB trp deletions at 37 C. At 42 C the frequency of tonB trp deletions in all K-12 strains approaches the low frequency observed for Ymel at 37 or 42 C. In contrast, spontaneous deletions in another region of the genome which simultaneously result in resistance to phages T7 and lambda and in proline auxotrophy (tfrA pro deletions) occur at a constant frequency regardless of growth temperature or the structure of the chromosome in the trp region. Two mutants of strain KB30 obtained after treatment with nitrosoguanidine show very low tonB trp deletion frequencies. The alterations in both mutants map in the trp region of the chromosome. These studies indicate that the structure of the cysB-trp-suIII region is responsible for many of the characteristic deletion frequencies observed.

Chromosome Aberrations↗

PubMed1971

Pseudomonas putida tryptophan synthetase: partial sequence of the subunit.

There is 50% identity in the sequences of the first 50 residues of the alpha chains of Escherichia coli and Pseudomonas putida. No deletions or additions of residues are found in this region, except for the N-terminal methionine residue which is missing in the polypeptide isolated from P. putida. Most of the residues which differ are chemically dissimilar, and half of them are specified by codons which differ by more than a single base. The two residues known by mutational analysis to be essential for catalysis in E. coli are conserved in P. putida. The potential taxonomic usefulness of information of this sort is analyzed.

Amino Acid Sequence↗

PubMed1971

Transcription of the operator proximal and distal ends of the tryptophan operon: evidence that trpE and trpA are the delimiting structural genes.

Measurements of the time required for transcription of regions of known genetic length in the tryptophan operon of Escherichia coli indicate that there are no major unidentified structural genes in the operon either before the operator proximal E gene or after the operator distal A gene.

Chromosome Mapping↗

PubMed1970