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Biomedical subjects

B Low

Publications and source records attributed to B Low.

7 recordsLinked to original sources
PubMed1979

Regulation of biosynthesis of aminoacyl-transfer RNA synthetases and of transfer-RNA in Escherichia coli.

We have isolated temperature resistant revertants from temperature sensitive E. coli strains containing either a thermolabile glutaminyl-tRNA synthetase or leucyl-tRNA synthetase. Among the revertants which still contained the thermolabile leucyl-tRNA synthetase we found two classes of regulatory mutants (leuX and leu Y) which have elevated levels of this enzyme. The leuX mutation specifies an operator-promoter region adjacent to the structural gene (leuS) for the enzyme. The leuY gene maps away from the leuS gene and codes for a protein. Using these mutants we demonstrated that the levels of leucyl-tRNA are related to the derepression of the leucine and isoleucine-valine operons. Among the revertants which still contained the thermolabile glutaminyl-tRNA synthetase were characterized three classes of mutants, glnT, glnU, and glnR. The glnT and glnU mutants contain elevated levels of tRNAgln, while the glnR mutant possesses elevated levels of glutaminyl-tRNA synthetase. The level of glutamine synthetase, the enzyme responsible for the formation of glutamine, is also derepressed in the glnT and glnR mutants.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Some genetic consequences of changes in the level of recA gene function in Escherichia coli K-12.

Genetic recombination was studied in E. coli mutants that carry lesions in the recA gene but retain some capacity for generating recombinant progeny. We observed that recombination was detectable only at a very low level during the incubation of leaky RecA- merozygotes in broth. However, recombination appeared to occur at much higher frequencies when recombinant progeny were assayed by selection on minimal agar. Analysis of the recombinants obtained with Hfr donors revealed a deficiency of multiple exchanges per unit length of DNA in leaky RecA- strains. In many of these crosses recombinants that inherited donor alleles close to the transfer origin were much reduced in frequency, except when the recipient was also RecB-.

Alleles↗
PubMed1975

Isolation and characterization of lambda transducing bacteriophages for the su1+ (supD minus) amber suppressor of Escherichia coli.

Specialized lambda transducing phages for the sul+ (supD-) amber suppressor in Escherichia coli K-12 have been isolated, using a secondary site lambda-cI857 lysogen in which we have shown the prophage to be closely linked to sul+.sul+ transducing particles were detected frequently, at 10-5 per plaque-forming unit, in lysates prepared from the secondary-site lysogens. High-frequency transducing lysates were obtained from several independently isolated sul+ transductants and were analyzed by CsCl equilibrium density gradient centrifugation. The transducing phages are defective; marker rescue analysis indicates that the lambda-N gene is not present. In lambda-cI857DELTANdSul+, a bio-type transducing phage, the genes specifying recombination and excision functions have been replaced by bacterial deoxyribonucleic acid.

Centrifugation, Density Gradient↗