Sequential action of factors involved in natural competence for transformation of Neisseria gonorrhoeae.

We previously identified and genetically characterized several factors essential for the natural competence of transformation in Neisseria gonorrhoeae. Here we analyse the sequential action of these factors and dissect the overall transformation process into three distinct steps, (i) the sequence-specific uptake of transforming DNA into a DNase-resistant state, (ii) the transfer of DNA to the cytosol and (iii) the processing and recombination of the incoming with the resident DNA. While two pilus-associated factors, PilE and PilC, were previously implicated in the early DNA uptake event, we show here that three competence factors unrelated to pilus biogenesis, ComA, ComL and Tpc, are not essential for DNA uptake and rather act in a subsequent step. The respective mutants, however, lack the characteristic nucleolytic processing observed with the incoming DNA in both wild-type and non-transformable RecA-deficient N. gonorrhoeae, indicating that they are blocked in the processing and/or the delivery of DNA to the cytoplasm. A hypothetical model proposing a sequential action of the known gonococcal competence factors is presented.