These data suggest that N. gonorrhoeae transformation by ssDNA is largely dependent on the presence of the Crick DUS12. A previous study reported efficient ssDNA transformation in N. gonorrhoeae much higher than the levels we measured

(Stein, 1991). This study did not report how much contaminating dsDNA was present in the ssDNA preparations, and therefore, those results are difficult to compare to the results obtained in this study. Our data show that there is significant dsDNA contamination of standard M13 ssDNA preparations and we added a column purification step to enrich for ssDNA molecules. It is possible that the high transformation efficiencies reported previously (Stein, 1991) were attributable to contaminating double-stranded BMS-354825 chemical structure RF DNA within the recombinant FDA approved Drug Library research buy M13 phage preparations. Our results support the observation of transformation in co-culture experiments with strains secreting ssDNA via the type IV secretion system (Dillard & Seifert, 2001). Interestingly,

Crick DUS0 ssDNA transformation was consistently, but not statistically higher than Watson DUS0 ssDNA transformation. We do not presently understand the reason why the Crick strand transforms consistently, but not statistically better without a DUS, but it could be used more efficiently during uptake or recombination into the chromosome or perhaps is more resistant to nucleases encountered during the transformation process. Although both the Watson and the Crick DUS12 sequences

enhanced transformation in both FA1090 and MS11, the magnitude of enhancement was much greater for the Crick DUS12 than the Watson DUS12 (Fig. 2). Again, these differences could be mediated at any stage in the transformation for process. The previously accepted model of dsDNA DUS12 action invokes the DUS12 sequence binding to a putative outer membrane receptor leading to increased DNA uptake into the periplasm. We have suggested that the DUS may have more complicated role during the process of transformation (Duffin & Seifert, 2010), which may include a role for the DUS beyond DNA uptake into the periplasm. Many factors are required for the complex process of transformation including DNA binding and DNA uptake into the periplasm and through the inner membrane. Prior reports have shown DUS12 dsDNA uptake is transported into the periplasm, but no reports have shown ssDNA transport. However, as all of the previous studies establish that the dsDUS mediates transport into the periplasm, we do not favor a role for the ssDUS in this step of transformation. A lack of activity in DNA uptake for ssDUS could explain the overall reduction in transformation of ssDNA compared to dsDNA.