Regulation of thymidine metabolism in Escherichia coli K-12: studies on the inducer and the coordinateness of induction of the enzymes

Multiple regulation of nucleoside catabolizing enzymes: effects of a polar dra mutation on the deo enzymes

Strains with an amber, polar mutation in the dra1 gene have been isolated. The mutation was introduced into a set of isogenic strains, wild type or with concurrent regulatory mutations, and further characterized by suppression and heat inactivation experiments. The effect of the polar dra mutation on the three remaining genes of the deo operon, the tpp, drm and pup genes, was determined by estimating the enzyme levels in the various dra-mutants. The effect was found to be non-coordinate, indicating the formation in the cells of two types of transcripts: A tetracistronic unit, containing the message from all four genes, and a dicistronic unit, covering the two distal genes only.

Conditional mutator gene in Escherichia coli: isolation, mapping, and effector studies

A mutator gene, mutD5, whose phenotype is conditional, has been identified in Escherichia coli. By P1 transduction it has been shown to lie at about 5.7 min on the chromosome, being co-transduced with proA and argF. In rich medium, streptomycin- and nalidixic acid-resistant mutation frequencies are 50 to 100 times higher than those in minimal medium. In minimal medium, the mutD5-induced mutation frequencies are still 50 to 100 times above co-isogenic wild-type (mut(+)) levels. Similar results were obtained with all markers tested. Mutant frequencies can be raised by thymidine in the medium at concentrations as low as 0.04 muM, or by the endogenous generation of thymidine from thymine plus a deoxyribosyl donor. Deoxyadenosine, various ribonucleosides, thymine, and 2-deoxyribose do not stimulate mutation. None of these effects are related to growth rate, since growth rate and mutation rate can be decoupled completely.