Antibody-mediated activation of a defective beta-D-galactosidase extracted from an Escherichia coli mutant.

Antibody-mediated Activation of a Defective Β-d-galactosidase

Two closely related protein antigens were used to study immunogenic competition. Namely, normal beta-D-galactosidase of Escherichia coli (Z) and a genetically defective beta-D-galactosidase (AMEF) which seems to differ from the normal in one amino acid substitution. A unique characteristic of this pair of antigens is that, although they are indistinguishable in precipitation and absorption test...

The beta-d-galactosidase of Escherichia coli, strain K-12.

Cloning and expression of the beta-D-galactosidase gene from Streptococcus thermophilus in Escherichia coli.

The beta-D-galactosidase (beta-gal) gene from Streptococcus thermophilus was cloned to isolate and characterize it for potential use as a selection marker in a food-grade cloning vector. Chromosomal DNA from S. thermophilus 19258 was cleaved with the restriction enzyme PstI and ligated to pBR322 for transformation into Escherichia coli JM108. A beta-galactosidase-positive clone was detected by ...

Septum formation-defective mutant of Escherichia coli.

Mutants of Escherichia coli defective in septum initiation, as well as in septum formation were obtained spontaneously, without mutagenic treatment, by selection of rifampin-tolerant mutants of an antibiotic-permeable strain carrying the envA mutation. The disturbed phenotype was in all mutants aggrevated the low incubation temperatures. One allele, sefA1, was studied in detail. Septum initiati...

Regulation of enzymatic activity in the intact cell: the beta-D-galactosidase of Escherichia coli.

Large differences in enzymatic activity are often found between intact cells and extracts. Lacking a better explanation, it has frequently been assumed that the penetration of the substrate is the rate limiting step in the intact cells. The experiments reported here were designed to test several hypotheses which might account for the discrepancy. The 3-galactosidase (lactase) in Escherichia col...