Cryptic plasmid of Neisseria gonorrhoeae: complete nucleotide sequence and genetic organization

The naturally occurring cryptic plasmid pJD1 of Neisseria gonorrhoeae is 4,207 base pairs long and is found in about 96% of gonococcal strains. The total probable coding capacity of pJD1 was determined from the complete nucleotide sequence by using computational probes to identify open reading frames with similar codon usage and by screening for the presence of ribosomal binding sites before the start codons. Candidates for promoters and terminators were also found in the sequence. Based on these findings, we propose a model for the genetic organization of the plasmid. The model predicts two transcriptional units, each composed of five compactly spaced genes. A promoter of one of the transcripts was shown to function in Escherichia coli, and the products of three of the five genes in this operon were identified in minicell expression experiments. Of these, the cppA gene encoded a 9-kilodalton protein, and the cppB and cppC genes both coded for 24-kilodalton proteins. No expression of the other transcriptional unit was detected, but two genes in this operon were expressed in minicells when transcribed from an E. coli promoter. The experimental data were consistent with the model.