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G D Hegeman

Publications and source records attributed to G D Hegeman.

At least 37 records · Page 2Linked to original sources
PubMed1971

Genetics of the mandelate pathway in Pseudomonas aeruginosa.

The linkage of genes governing synthesis of enzymes functional in the conversion of l(+)-mandelate to benzoate in Pseudomonas aeruginosa was studied. These genes were found to be linked in a fashion consistent with regulatory mechanisms known to govern synthesis of this inducible pathway. Surprisingly, linkage was also observed between the mandelate genes and those governing the synthesis of functionally related enzymes that participate in the catabolism of anthranilate and benzoate. These latter genes are grouped in at least three regulatory units. Some theoretical explanations for high intensity of linkage among functionally related genes whose expression is not induced by a common metabolite are discussed.

Benzoates↗
PubMed1971

Tumor induction by Agrobacterium tumefaciens: specific transfer of bacterial deoxyribonucleic acid to plant tissue.

When Agrobacterium tumefaciens cells grown in the presence of tritiated thymidine to label specifically the bacterial deoxyribonucleic acid (DNA) are incubated with carrot root tissue for short periods of time, an appreciable fraction of the label becomes firmly associated with the root tissue. Such association is not observed in identical experiments when A. tumefaciens cell ribonucleic acid or protein are labeled. The extent of the retention of thymidine-derived label from bacterial cells by the root tissue in experiments with A. radiobacter and poorly tumorigenic strains of A. tumefaciens is significantly less than that afforded by tumorigenic strains of A. tumefaciens but greater than the level afforded by Escherichia coli. Transfer of DNA-specific label from A. tumefaciens to carrot root discs is not enhanced by treatments designed to provoke lysis of the bacterial cells, nor is it decreased by addition of deoxyribonuclease or excess unlabeled thymidine to the incubation medium. Bacterial cell-to-plant cell contact is necessary for transfer. Unlabeled A. radiobacter cells decrease in a competitive manner transfer of label when mixed with labeled A. tumefaciens cells. These findings suggest that transfer of DNA from A. tumefaciens to plant tissue after binding of the bacterial cells to specific plant tissue site(s) is a necessary feature of the mechanism by which A. tumefaciens provokes tumors in plants and provides an experimental technique of potentially great value in study of the early steps in the process of tumor induction by A. tumefaciens.

Animals↗
PubMed1969

Phenol and benzoate metabolism by Pseudomonas putida: regulation of tangential pathways.

Catechol occurs as an intermediate in the metabolism of both benzoate and phenol by strains of Pseudomonas putida. During growth at the expense of benzoate, catechol is cleaved ortho (1,2-oxygenase) and metabolized via the beta-ketoadipate pathway; during growth at the expense of phenol or cresols, the catechol or substituted catechols formed are metabolized by a separate pathway following meta (2,3-oxygenase) cleavage of the aromatic ring of catechol. It is possible to explain the mutually exclusive occurrence of the meta and ortho pathway enzymes in phenol- and benzoate-grown cells of P. putida on the basis of differences in the mode of regulation of these two pathways. By use of both nonmetabolizable inducers and blocked mutants, gratuitous synthesis of some of the meta pathway enzymes was obtained. All four enzymes of the meta pathway are induced by the primary substrate, cresol or phenol, or its analogue. Three enzymes of the ortho pathway that catalyze the conversion of catechol to beta-ketoadipate enol-lactone are induced by cis,cis-muconate, produced from catechol by 1,2-oxygenase-mediated cleavage. Observations on the differences in specificity of induction and function of the two pathways suggest that they are not really either tangential or redundant. The meta pathway serves as a general mechanism for catabolism of various alkyl derivatives of catechol derived from substituted phenolic compounds. The ortho pathway is more specific and serves primarily in the catabolism of precursors of catechol and catechol itself.

Acetates↗
PubMed1968

Genetic control of the beta-ketoadipate pathway in Pseudomonas aeruginosa.

The regulation and genetic control of the beta-ketoadipate pathway in Pseudomonas aeruginosa were investigated. The pattern of enzyme induction is apparently the same as in P. putida. Mutants were obtained for all but 1 of the 11 structural genes; the proximity of these genes on the chromosome was examined by transduction of the mutants with phage F116. If a group of enzymes was induced by the same compounds, the corresponding genes were closely clustered. Surprisingly, some locispecifying enzymes not sharing a common inducer were also clustered. It is suggested that this latter finding may indicate a degree of chromosomal specialization.

Adipates↗
PubMed1966

Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. I. Synthesis of enzymes by the wild type.

Hegeman, G. D. (University of California, Berkeley). Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida. I. Synthesis of enzymes by the wild type. J. Bacteriol. 91:1140-1154. 1966.-The control of synthesis of the five enzymes responsible for the conversion of d(-)-mandelate to benzoate by Pseudomonas putida was investigated. The first three compounds occurring in the pathway, d(-)-mandelate, l(+)-mandelate, and benzoylformate, are equipotent inducers of all five enzymes. A nonmetabolizable inducer, phenoxyacetate, also induces synthesis of these enzymes; but, unlike the metabolizable inducer-substrates, it does not elicit synthesis of enzymes that mediate steps in the pathway beyond benzoate. Under conditions of semigratuity, dl-mandelate elicits immediate synthesis at a steady rate of the first two enzymes of the pathway, but two enzymes which act below the level of benzoate are synthesized only after a considerable lag. Succinate and asparagine do not significantly repress the synthesis of the enzymes responsible for mandelate oxidation.

Asparagine↗