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C Yanofsky

Publications and source records attributed to C Yanofsky.

At least 235 records · Page 13Linked to original sources
PubMed1974

Suppression of glutamic acid codons by mutant glycine transfer ribonucleic acid.

In previous mutational studies with mutant trpA46 (Gly [GGA] --> Glu [GAA] at position 211 of the tryptophan synthetase alpha chain) of Escherichia coli, no missense suppressors were detected. Such suppressors have now been obtained by single mutations in gly Vins, the structural gene for a GGA/G-reading, mutationally altered form of gly V transfer ribonucleic acid (tRNA) (tRNA(Gly) which reads GGU/C). A trpA46 strain containing the gly Vins alteration was mutagenized with hydroxylamine, and suppressor mutations were detected in the prototrophs obtained. Eighteen independent suppressors were examined and shown to have alterations which map in the gly V region. Chromatography of the glycyl-tRNAs of one suppressed mutant on a benzoylated diethylaminoethyl-cellulose column revealed an alteration in the tRNA(ins) (Gly) peak. The trpA46 suppressor mutation thus appears to involve a change of tRNA(ins) (Gly) from a GGA/G (Gly) reader to a GAA (Glu) reader. Since this suppressor presumably retains the "wobble" pairing of gly Vins tRNA, it was used to select the conversion of GAU (Asp211) to GAG (Glu211) in the alpha chain. supD (serine-inserting amber suppressor) was then used to obtain the conversion of GAG (Glu211) to UAG211. Missense revertants of trpA (UAG211) are being isolated as a means of introducing new codons which can be used in the selection of additional missense suppressors.

Amino Acids↗
PubMed1974

Structural interactions between amino acid residues at positions 22 and 211 in the tryptophan synthetase alpha chain of Escherichia coli.

Construction and characterization of double mutants altered in the structural gene of the tryptophan synthetase alpha chain of Escherichia coli revealed interactions between amino acid residues at positions 22 and 211. These interactions are specific for the particular amino acid residue at position 211. The results indicate also that amino acid residues which appear to be functionally near-equivalent in one configuration may strongly influence the activity of a protein with a subsequent change at another site. Seven independent suppressors of trpA218 (Leu22-Ser211) were isolated. Their properties suggest that all seven may suppress the codon (AGU/C) for Ser211. Six of the seven are co-transducible with glyV, the structural gene for the GGU/C-specific tRNA(Gly).

Amino Acids↗
PubMed1974

Localization of two functions of the phosphoribosyl anthranilate transferase of Escherichia coli to distinct regions of the polypeptide chain.

The trpD gene specifies a polypeptide which has both glutamine amidotransferase and phosphoribosyl anthranilate (PRA) transferase activities. Deletions fusing segments of trpD to the gene preceding it in the operon, trpE, were selected in strains carrying various trpD point mutations. The selection procedure required both that a deletion enter trpE and that it restore the PRA transferase activity which the parent trpD point mutant lacked. Deletion mutants were found which had PRA transferase activity although the first third of trpD was deleted. The existence of the mutants proves that a terminal segment of trpD is sufficient to specify a polypeptide having PRA transferase activity. The location of the deletion end points on the genetic map of trpD defines the extent of the trpD segment required for PRA transferase activity. This segment did not overlap the initial region of trpD required to specify the glutamine amidotransferase function of the trpD polypeptide. These results support the hypothesis (M. Grieshaber and R. Bauerle, 1972; H. Zalkin and L. H. Hwang, 1971) that the bifunctional trpD polypeptide might have evolved by fusion of a gene specifying a glutamine amidotransferase with a gene directing PRA transferase synthesis.

Ammonia↗
PubMed1974

Isolation and characterization of specialized phi80 transducing phages carrying regions of the Salmonella typhimurium trp operon.

We have isolated a series of nondefective phi80 specialized transducing phage which carry segments of the Salmonella typhimurium trp operon. These phage were obtained from a lysogenic derivative of a merozygote constructed by transferring an S. typhimurium trp episome into an Escherichia coli strain which lacks the normal phi80 attachment site. The deoxyribonucleic acid (DNA) from one such phage was purified and employed in DNA-ribonucleic acid (RNA) hybridization studies. The results obtained show that, under our hybridization conditions, heterologous hybridization is less efficient than homologous hybridization. It was also observed that not all S. typhimurium trp messenger RNA can readily anneal to E. coli trp operon DNA. Heterologous hybrids consisting of S. typhimurium trp messenger RNA and E. coli trp operon DNA were estimated to have a dissociation constant 10-fold larger than that of homologous hybrids.

Chromosome Mapping↗
PubMed1973

Nucleotide sequence divergence in the -chain-structural genes of tryptophan synthetase from Escherichia coli, Salmonella typhimurium, and Aerobacter aerogenes.

Two different estimates were obtained for the extent of nucleotide sequence divergence in the structural genes of the tryptophan synthetase alpha-chains of Escherichia coli, Salmonella typhimurium, and Aerobacter aerogenes. One estimate was based on comparisons of the amino acid sequences of the respective alpha chains. The other was derived from measurements of the thermal stability of RNA-DNA hybrids formed with phage DNA carrying the alpha-chain structural gene of E. coli and labeled messenger RNA from the three bacterial species. Comparison of the two estimates suggests that during the course of evolution synonymous codon changes have accumulated in the alpha-chain-structural genes.

Amino Acid Sequence↗
PubMed1973

Nucleotide sequences from tryptophan messenger RNA of Escherichia coli: the sequence corresponding to the amino-terminal region of the first polypeptide specified by the operon.

Mutants with internal deletions that terminate near the operator end of the tryptophan operon of E. coli were used in studies on the nucleotide sequence at the 5' end of the messenger RNA transcribed on this operon. The findings obtained permitted identification of a sequence of 43 nucleotides corresponding to the aminoterminal 11 amino acids of anthranilate synthetase component I, the polypeptide specified by the operator-proximal structural gene of the operon. It was also shown that the translation initiation codon for this polypeptide is preceded on the messenger by a "leader" sequence of unknown function, at least 150 nucleotides in length.

Amino Acid Sequence↗
PubMed1973

Duplication-translocations of tryptophan operon genes in Escherichia coli.

Mutants of Escherichia coli were selected in which a single mutational event had both relieved the polar effect of an early trpE mutation on trpB and simultaneously released the expression of trpB from tryptophan repression. The frequency at which these mutations appeared was roughly equal to the frequency of point mutations. In each of these mutants, the mutation increased the function of trpB and also increased the activity of some, but not all, of the other four tryptophan operon genes. Genetic analysis showed that the mutations were not located within the trp operon since in each case the parental trp operon could be recovered from the mutants. Each mutant was shown to carry a duplication of a trp operon segment translocated to a new position near the trp operon. Polarity is relieved since the trpB duplication-translocation is not in the same operon as the trpE polar mutation. The duplicated and translocated segments are fused to operons not regulated by tryptophan, so trpB function is no longer subject to tryptophan repression. The properties of the mutants indicate that the length of the duplicated segment and the position to which it is translocated differ in each of the seven mutants studied. The duplications are unstable, but the segregation pattern observed is not consistent with a single crossover model for segregation. That such duplication-translocation events generate a variety of new genetic arrangements at a frequency comparable with point mutations suggests they may play an important role in evolution.

Chromosome Mapping↗