Porin protein of Neisseria gonorrhoeae: cloning and gene structure.

The outer membrane porin molecule of Neisseria gonorrhoeae is known as protein I (PI). Among different strains of gonococci there is variability of PI, and two main classes, PIA and PIB, have been recognized. A lambda gt11 bank of gonococcal DNA was screened using monoclonal antibodies directed to a PIB-type porin molecule of N. gonorrhoeae, and three immunoreactive clones were isolated. DNA sequence analysis indicated that each contained only portions of the PI structural gene, but that together they contained the complete gene, and its structure was determined. The DNA sequence predicts a protein of 348 amino acids with a typical 19 amino acid signal peptide. The PI protein resembles Escherichia coli porins in size, lack of long hydrophobic sequences, and absence of cysteine residues. Sequence homologies between PI and the E. coli porins were found, particularly in the 100 N-terminal and the 110 C-terminal amino acids. In addition to the coding sequence of PI, the complementary strand contains a large open reading frame. At the 3' end of the PI gene, immediately following an inverted repeat (probably the transcription terminator), the clone contains an unusual sequence consisting of 31 perfect repeats of the heptamer CTGTTTT. Hybridization analysis suggests that there is a single structural gene for PI and that it is homologous to the gene found in a PIA-bearing strain of gonococcus.