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Biomedical subjects

B G Hall

Publications and source records attributed to B G Hall.

81 records · Page 5Linked to original sources
PubMed1977

A third beta-galactosidase in a strain of Klebsiella that possesses two lac genes.

Klebsiella strain RE1544 contains two lac operons, one on the chromosome and one on a lac plasmid. A mutant of RE1544, in which the lacZ genes of both operons produce no active enzyme, was found to synthesize a beta-galactosidase that hydrolyzes ortho-nitrophenyl-beta-D-galactopyranoside but not lactose. Synthesis of this beta-galactosidase (BGase-III) is induced by lactose but not by isopropyl-1-thio-beta-D-galactopyranoside or methyl-beta-D-thiogalactopyranoside. In both the regulation of synthesis and substrate specificity, BGase-III strongly resembles the ebg0 enzyme of Escherichia coli. Nevertheless, by the criteria of immunological cross-reactivity and subunit molecular weight, BGase-III is not related to the ebg0 enzyme.

Cross Reactions↗
PubMed1976

Methyl galactosidase activity: an alternative evolutionary destination for the ebgA0 gene.

Previous studies (Campbell et al., 1973; Hall and Hartl, 1974; Hall and Hartl, 1975) have shown that the ebgA0 gene, whose product does not hydrolyze lactose may evolve so that its product does hydrolyze lactose; i.e., lactase activity is one evolutionary destination of the ebgA0 gene. Beginning with a strain that synthesizes ebgA0 gene product constitutively and grows extremely slowly (doubling time, 30 to 50 h) on methyl-beta-D-galactopyranoside (MG), a derivative was selected capable of growth on MG at a moderate rate (doubling time, 5.9 h). Genetic evidence is presented showing that the gene that permits growth on MG is an allele of ebgA. A comparison among strains bearing several alleles of ebgA shows that the new allele, termed ebgAmg, synthesizes a product specific for MG and thus represents a true alternative evolutionary destination for the ebgA0 gene.

Alleles↗
PubMedDate not supplied

Evolution of a regulated operon in the laboratory.

The evolution of new metabolic functions is being studied in the laboratory using the EBG system of E. coli as a model system. It is demonstrated that the evolution of lactose utilization by lacZ deletion strains requires a series of structural and regulatory gene mutations. Two structural gene mutations act to increase the activity of ebg enzyme toward lactose, and to permit ebg enzyme to convert lactose into allolactose, and inducer of the lac operon. A regulatory mutation increases the sensitivity of the ebg repressor of lactose, and permits sufficient ebg enzyme activity for growth. The resulting fully evolved ebg operon regulates its own expression, and also regulates the synthesis of the lactose permease.

Biological Evolution↗