An inhibitor of DNA binding and uptake events dictates the proficiency of genetic transformation in Neisseria gonorrhoeae:: mechanism of action and links to Type IV pilus expression

Although natural genetic transformation is a widely disseminated form of genetic exchange in prokaryotic species, the proficiencies with which DNA recognition, uptake and processing occur in nature vary greatly. However, the molecular factors and interactions underlying intra- and interspecies diversity in levels of competence for natural genetic transformation are poorly understood. In Neisseria gonorrhoeae, the Gram-negative aetiologic agent of gonorrhoea, DNA binding and uptake involve components required for Type IV pilus (Tfp) biogenesis as well as those which are structurally related to Tfp biogenesis components but dispensable for organelle expression. We demonstrate here that the gonococcal PiIV protein, structurally related to Tfp pilin subunits, is an intrinsic inhibitor of natural genetic transformation which acts ultimately by reducing the levels of sequence-specific DNA uptake into the cell. Specifically, we show that DNA uptake is enhanced in strains bearing piIV mutations and reduced in strains overexpressing PiIV. Furthermore, we show that PiIV exerts its effect by acting as an antagonist of ComP, a positive effector of sequence-specific DNA binding. As it prevents the accumulation of ComP at a site where it can be purified by shear extraction of intact cells, the data are most consistent with PiIV either obstructing ComP trafficking or altering ComP stability. In addition, we report that ComP and PiIV play overlapping and partially redundant roles in Tfp biogenesis and document other genetic interactions between comP and piIV together with the piIE and piIT genes required for the expression of retractile Tfp. Together, the results reveal a novel mechanism by which the levels of competence are governed in prokaryotic species and suggest unique ways by which competence might be modulated.