Enzyme synthesis following conjugation and recombination in Escherichia coli

Abstract

The structural gene for alkaline phosphatase, when injected by an Hfr into a constitutive recipient, does not function extensively. After an initial spurt, phosphatase synthesis suffers an eclipse and is not resumed until the P⁺ gene is integrated into the recipient's chromosome. The time-course of genetic recombination was investigated by following the synthesis of alkaline phosphatase in crosses between allelic phosphatase-negative mutants. The appearance of PP⁺ recombinant nuclei in such crosses is paralleled by an increase in the differential rate of enzyme synthesis. Functional recombinants arise 30 to 40 minutes after the entry of the Hfr P gene and multiply exponentially from the time they originate. The kinetics of recombination are unrelated to the generation time of the F⁻. In a recipient carrying a thermosensitive mutation which blocks DNA replication at 42°C, recombination occurs in the absence of DNA replication. Interference with DNA replication, in fact, greatly enhances the rate of recombination.