Search PubMed⌕ Search

Biomedical subjects

C Yanofsky

Publications and source records attributed to C Yanofsky.

At least 163 records · Page 9Linked to original sources
PubMed1982

Regulatory region of the Klebsiella aerogenes tryptophan operon.

The trp operon of Klebsiella aerogenes was cloned, and its regulatory region was sequenced. Comparison with previously reported trp regulatory sequences of other enteric bacteria indicates that the K. aerogenes trp promoter-operator region is most similar to the corresponding region of Salmonella typhimurium. The trp leader regions of K. aerogenes and other enteric bacteria are organized similarly, but there are significant differences in the stabilities of the predicted secondary structures in their leader transcripts. These differences should make the K. aerogenes attenuator a weaker transcription termination site than any of the other attenuator regions studied; this was confirmed in in vitro transcription experiments. The sequence of the leader transcript and the precise site of in vitro termination were determined.

Base Sequence↗
PubMed1982

Evolutionary divergence of the Citrobacter freundii tryptophan operon regulatory region: comparison with other enteric bacteria.

The regulatory region of the trp operon of Citrobacter freundii was sequenced and compared with the corresponding regions of other enteric bacteria. Significant differences were noted in the promoter region. These differences are presumably responsible for the weak expression of the cloned trp operon in Escherichia coli. The presumed operator region, although nonfunctional in E. coli, has dyad symmetry, but the sequence of the symmetrical region differs appreciably from those of operators that can be regulated by the E. coli trp repressor. The sequence of the trp leader region of C. freundii resembles that of other enteric bacteria, suggesting that the C. freundii operon is also regulated by attenuation. Comparison of the sequence of the initial portion of trpE with the homologous regions of E. coli and Salmonella typhimurium indicates that the three organisms probably are evolutionary equidistant.

Anthranilate Synthase↗
PubMed1981

The complete nucleotide sequence of the tryptophan operon of Escherichia coli.

The tryptophan (trp) operon of Escherichia coli has become the basic reference structure for studies on tryptophan metabolism. Within the past five years the application of recombinant DNA and sequencing methodologies has permitted the characterization of the structural and functional elements in this gene cluster at the molecular level. In this summary report we present the complete nucleotide sequence for the five structural genes of the trp operon of E. coli together with the internal and flanking regions of regulatory information.

Base Sequence↗
PubMed1981

Pausing of RNA polymerase during in vitro transcription of the tryptophan operon leader region.

RNA polymerase molecules pause at a single site during in vitro transcription of the tryptophan (trp) operon leader region. Pausing was observed when DNA templates derived from Escherichia coli. Salmonella typhimurium, and Klebsiella aerogenes were used. Fingerprint analyses showed that the major RNA species produced by the transcriptional pause is 91 nucleotides long. A minor RNA species 90 nucleotides long was also detected. Single-round transcription experiments were used to study the kinetics of pausing. Time course, pulse-chase, and delayed-labeling experiments suggest that every RNA polymerase molecule transcribing the trp leader region pauses. A suboptimal ribonucleoside triphosphate concentrations, the half-life of paused-leader RNA was approximately 3 min at 22 degrees C and 0.7 min at 37 degrees C. At near-optimal ribonucleoside triphosphate concentrations, the half-time of the paused species dropped to about 0.3 min at 22 degrees C. The appearance and half-life of the paused species were unaffected by salt concentration, rho factor, guanosine 3'-5'-bis(diphosphate), or point mutations in the trp attenuator region. It is postulated that transcriptional pausing may play a role in maintaining the synchronization of transcription and translation that is vital in the control of transcription termination at the trp operon attenuator.

Adenosine Triphosphate↗
PubMed1981

Comparison of the nucleoside sequence of trpA and sequences immediately beyond the trp operon of Klebsiella aerogenes. Salmonella typhimurium and Escherichia coli.

The nucleotide sequence of trpA of Klebsiella aerogenes is presented and compared with the trpA sequences of Salmonella typhimurium and Escherichia coli. The majority of the approximately 200 differences between each pair of trpA's are single nucleotide pair changes that do not alter the amino acid sequence. Codon usage conforms to the general patterns revealed by examination of other prokaryotic gene sequences. However, codon usage in K. aerogenes trpA reflects the high G+C content of the genome of this organism. The DNA sequences just beyond trpA, the presumed transcription termination region, are also compared for the three species. Perusal of these sequences indicates that the secondary structure of the transcript segment just beyond trpA has been preserved, while the primary sequence has diverged appreciably.

Amino Acid Sequence↗
PubMed1981

Attenuation in the control of expression of bacterial operons.

Bacterial operons concerned with the biosynthesis of amino acids are often controlled by a process of attenuation. The translation product of the initial segment of the transcript of each operon is a peptide rich in the amino acid that the particular operon controls. If the amino acid is in short supply translation is stalled at the relevant codons of the transcript long enough for the succeeding segment of the transcript to form secondary structures that allow the transcribing RNA polymerase molecule to proceed through a site that otherwise dictates termination of transcription. This site is the attenuator; the process is attenuation.

Amino Acids↗
PubMed1981

Dispersed 5S RNA genes in N. crassa: structure, expression and evolution.

The 5S RNA genes (5S genes) in N. crassa are not tandemly arranged or tightly clustered as in other eucaryotes that have been examined. 55 RNA or cloned 5S DNA hybridizes to at least 30 different restriction fragments of Neurospora DNA. Of 34 5S DNA clones examined, each contains a single 5S gene. Saturation hybridization analyses indicate that there are about 100 copies of 5S genes in the genome of this organism. We have partially or completely sequenced the 5S region of 15 clones. Both identical and highly divergent 5S coding regions were found. Nine are of one type (alpha). The other six include four different types (beta, beta', gamma and delta) which differ from each other and from the alpha genes to various degrees. Eleven of 15 genes have distinct flanking regions. Analysis of Neurospora 5S RNA showed that it consists of one principal species which matches the alpha-type gene sequence. Additional 5S species corresponding to the less abundant 5S gene types were also detected. The pattern of nucleotide substitutions between the predicted Neurospora 5S RNAs and between these and S. cerevisiae 5S RNA suggests that a particular 5S RNA secondary structure occurs in vivo and is conserved.

Base Sequence↗
PubMed1981

Procedure for production of hybrid genes and proteins and its use in assessing significance of amino acid differences in homologous tryptophan synthetase alpha polypeptides.

Hybrid tryptophan synthetase alpha and beta polypeptides were produced by genetic recombination between the trpB--trpA regions of Escherichia coli and Salmonella typhimurium contained on compatible, multicopy plasmids. Intragenic recombination was decreased but still evident in recA cells. Genetic exchange occurred at many sites within trpA, but every recombinant gene produced a functional alpha polypeptide despite many amino acid differences from one or the other of the parental polypeptides. The five hybrid tryptophan synthetase alpha subunits examined resembled the parental polypeptides in catalytic function but differed in thermostability. The stability differences suggest that, as amino acid changes occurred in these proteins during the course of evolution, subsequent changes were limited to those that would allow retention of a desired protein conformation.

Amino Acid Sequence↗
PubMed1981

Rifampin resistance mutations that alter the efficiency of transcription termination at the tryptophan operon attenuator.

Rifampin-resistant mutants of Escherichia coli were isolated which had altered patterns of resistance or sensitivity to the inhibitory compounds 5-methyltryptophan and 5-methylanthranilate. The levels of tryptophan (trp) operon polypeptides in different rifampin-resistant mutants were elevated or reduced, in a manner consistent with their sensitivity to the two analogs. Complementation tests established that the mutations were in rpoB, the structural gene for the beta subunit of ribonucleic acid polymerase. Introduction of these rpoB mutations into mutant strains which terminate transcription abnormally at the trp operon attenuator established that the rpoB mutations alter trp operon expression by increasing or decreasing transcription termination at the attenuator. The rpoB mutations affected transcription termination at the attenuator only in strains which were able to form what is thought to be a ribonucleic acid termination structure. These findings suggest that alteration of the beta subunit of ribonucleic acid polymerase directly or indirectly affects ribonucleic acid polymerase's recognition of the transcription termination signal at the trp operon attenuator.

DNA-Directed RNA Polymerases↗
PubMed1981

Nucleotide sequence of the structural gene for tryptophanase of Escherichia coli K-12.

The tryptophanase structural gene, tnaA, of Escherichia coli K-12 was cloned and sequenced. The size, amino acid composition, and sequence of the protein predicted from the nucleotide sequence agree with protein structure data previously acquired by others for the tryptophanase of E. coli B. Physiological data indicated that the region controlling expression of tnaA was present in the cloned segment. Sequence data suggested that a second structural gene of unknown function was located distal to tnaA and may be in the same operon. The pattern of codon usage in tnaA was intermediate between codon usage in four of the ribosomal protein structural genes and the structural genes for three of the tryptophan biosynthetic proteins.

Amino Acid Sequence↗
PubMed1981

Cloning and characterization of the gene for Escherichia coli tryptophanyl-transfer ribonucleic acid synthetase.

From a Clark-Carbon plasmid containing trpS, the structural gene for the tryptophanyl-transfer ribonucleic acid synthetase of Escherichia coli, we subcloned a 2.6-kilobase fragment that has trpS and its neighboring regions. The location and orientation of trpS in the deoxyribonucleic acid insert was determined by deoxyribonucleic acid sequencing. In vitro transcription experiments and S1 nuclease mapping studies with in vivo message established that transcription is initiated at the same site in vivo and in vitro, approximately 58 base pairs upstream from the trpS coding region. We also describe the construction of an inphase trpS-lacZ gene fusion that is under the control of the trpS promoter and encodes a hybrid protein with beta-galactosidase activity.

Amino Acyl-tRNA Synthetases↗