On the Expression of a Structural Gene

Abstract

Experiments were made on the kinetics of β-galactosidase production by zygotes formed upon mating of inducible, lac+(Hfr z+i+), and constitutive, lac−(F−z−i−), strains of Escherichia coli K12. Enzyme formation commenced within two minutes of the time of injection of the z+ gene. The zygote thereafter produced β-galactosidase at a rate similar to that by an induced bacterium, and no increase in rate of enzyme production per zygote was observed in the first thirty minutes after mating. Therefore, the time required for the injected genetic material to become active in the functional apparatus of the F− cell, for formation of any possible intermediates between genetic material and enzyme, and for formation of the enzyme itself, are each less than two minutes. The Hfr strain of E. coli was labeled with 32P and was mated with the non-radioactive F− bacteria. A segment of 32P-labeled genetic material containing the z+ locus was transferred to the recipient. 32P decay in the newly acquired genetic material was found to decrease the enzyme-forming capacity of zygotes even when it occurred some time after initiation of enzyme synthesis. These results appear to indicate that integrity of the genetic material is required not only for an initial transfer of genetic information, but actually for enzyme synthesis to continue.