Preferential uptake of restriction fragments from a gonococcal cryptic plasmid by competent Neisseria gonorrhoeae

Factors involved in the specificity of DNA uptake by competent Neisseria gonorrhoeae were examined. Host-controlled modification did not affect uptake. Certain restriction fragments of the 4.2 kb gonococcal cryptic plasmid pFA1 and of the replicative form of the bacteriophage M13 were taken up in preference to others, independent of differences in fragment size. A 600 bp fragment from the 4.2 kb plasmid was cloned into pLES2, a gonococcal-Escherichia coli shuttle vector; the 600 bp fragment was taken up into a DNAase-I-resistant state in preference to the vector fragment. A second 370 bp fragment in pFA1 was also taken up preferentially. The 600 bp and 370 bp fragments share a 10 bp sequence, which is found in pFA1 only on fragments that were taken up readily. However, a fragment from M13 which was efficiently taken up did not contain this 10 bp sequence. In addition, this sequence was not sufficient to direct preferential DNA uptake by gonococci, since a recombinant plasmid containing this 10 bp sequence was not taken up appreciably better than the vector plasmid or another recombinant plasmid containing an unrelated 10 bp sequence. Sequence comparisons of the three restriction fragments which were preferentially taken up did not yield any consensus sequences greater than 7 bp. Although it is likely that efficient uptake of DNA by gonococci is determined by DNA structure, a single short sequence could not be found that accounted for specific uptake.