The class 2 protein of Neisseria meningitidis is the major outer membrane protein and a porin. A lambda gt11 bank of meningococcal chromosomal DNA was screened with monoclonal antibodies against gonococcal protein IB that cross-react with meningococcal class 2 protein. Three independent immunoreactive clones were isolated. DNA sequence analysis indicated that these clones included regions encoding the N-terminal portion of the class 2 protein. An oligonucleotide of 21 bases that was complementary to this sequence was synthesized and used as a probe for a second screening of the lambda gt11 bank. One of the positive clones isolated contained the complete gene, including the ribosome binding site, but lacked the promoter region. On the basis of the DNA sequence, a protein of 360 amino acids was predicted. Comparison of the predicted protein sequence with that of gonococcal protein I showed little homology in six regions constituting 29% of the total amino acids, while the remainder of the coding frame showed 81% homology of amino acid residues. The DNA homology in the immediate 5' and 3' noncoding sequences was very striking. Following the putative transcription terminator, the 3' DNA sequence contained a complex pattern of direct and inverted repeats having some similarity to the 3' sequence of the gonococcal protein IB gene and very close homology to a sequence located in the pilS1 region (R. Haas and T. F. Meyer, Cell 44:107, 1986), an area of the gonococcal genome containing silent pilin genes.

We have determined the DNA sequence of a cloned gonococcal gene and found that the predicted protein sequence is highly homologous to the class of blue copper-containing proteins known as azurins. However, the 127 amino acid sequence homologous to azurin is preceded by two unusual structural features. The gene possesses a typical 17 residue lipoprotein signal peptide and the N-terminal 39 amino acids are very rich in proline and alanine. The azurin gene of Pseudomonas aeruginosa has recently been characterized and possesses an ordinary signal peptide susceptible to signal peptidase I, causing export of a soluble protein to the periplasm. In gonococcus it would appear that the homologous product becomes an outer membrane protein.

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.