Loss of an Essential Function of Escherichia coli by Deletions in the thyA Region

Abstract

In an attempt to obtain deletions in the thyA gene, an abnormal lysogen of λ having the prophage inserted between the thyA and lysA genes was induced, and the surviving cured cells were examined for Thy − and Lys − mutants. In nearly 10,000 cured cells, 184 Lys − but no Thy − mutants were found. At the same time, the induced λ phage contained an approximately equivalent number of λ thyA + and λ lysA + transducing particles. By contrast, in a strain with the genotype F′ thyA − lysA + / thyA + lysA + , induction of the abnormal λ lysogen gave rise to many Thy − mutants in the cells cured of the prophage. In these Thy − mutants it was not possible to eliminate the episome with acridine orange, although the episome could be removed in control cultures with a thyA + allele in the resident gene. Therefore, it was suggested that deletion of a gene in the region of the chromosome from the position of the insertion of the λ prophage through the thyA gene caused loss of an essential and diffusible function.