A Thermolabile Repression System
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Excerpt
We have isolated an E. coli mutant in which the regulatory system controlling the synthesis of β-galactosidase has become thermolabile (Horiuchi, Horiuchi and Novick, 1961). This mutant, called E103, is derived from E102, a methionine-requiring Cavalli Hfr strain (Horiuchi, Tomizawa, and Novick, 1961).
At lower temperatures the mutant is like the wild-type strain in being inducible, i.e., a specific inducer is required for the synthesis of β-galactosidase. At higher temperatures it resembles a constitutive mutant, i.e., β-galactosidase is made at high rates independent of the presence of inducer. For example, β-galactosidase is made by E103 at 14° at 0.5% of maximum rate and at 43.5° at about 40% of maximum. In comparison, this enzyme is made by the wild type (E10.2) at about 0.1% of maximum at both temperatures. In the presence of inducer, both E103 and E102 make β-galactosidase at full rate at both temperatures. Also, a typical constitutive...
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* On leave from the National Institute of Health of Japan, Tokyo, Japan.
