Requirements for suppression of a dnaG mutation by an I-type plasmid

Abstract

The phenomenon of suppression of a dnaG mutation [in Escherichia coli] was confirmed and further characterized by an I plasmid and the requirements for the complete expression of suppressibility were determined. The authentic derepressed mutation of the conjugal fertility system, described earlier, was 1 of the requirements. The 2nd requirement is a previously undescribed type of mutation leading to a far higher degree of derepression of this system than the authentic drd mutation. This 2nd mutation leads to extremely high conjugal fertility and pilus production. A 3rd requirement for the complete expression of suppressibility is that the host recA function remain intact. recA function is required not merely for the fulfillment of the other 2 requirements described above, but also for an additional step or steps leading to its complete expression. The nature of this step(s) is unknown, but it is not insertion of the plasmid into the host genome.