Cloning and sequencing of a Moraxella bovis pilin gene

Moraxella bovis pili have been shown to play a major role in both infectivity and protective immunity of bovine infectious keratoconjunctivitis. Sonicated M. bovis DNA from the piliated strain EPP63 was inserted into the vector lambda gt11 with EcoRI linkers. Recombinant phage were screened with an oligonucleotide probe based on the amino-terminal portion of the DNA sequence of a Neisseria gonorrhoeae pilin gene. Two candidate phages produced a protein that comigrated with EPP63 beta pilin in sodium dodecyl sulfate-polyacrylamide gels and bound anti-pilus antisera. The 1.9-kilobase insert from one of these, lambda gt11M182, was subcloned in both orientations into pBR322, forming the plasmids pMxB7 and pMxB9, both of which produced beta pilin, as did pMxB12, a HindIII deletion derivative of pMxB7. In HB101(pMxB12), the M. bovis pilin protein was shown to be primarily localized in the inner membrane. The entire 939-base-pair insert of pMxB12 was sequenced, revealing a ribosome binding site just upstream of the coding region and an AT-rich region further upstream containing some potential RNA polymerase recognition sites. The translation of the sequence predicts a six-amino-acid leader sequence preceding the phenylalanine that begins the mature protein. Codon usage analysis of the M. bovis beta pilin gene revealed greater use of the CUA codon for leucine than usual for a well-expressed Escherichia coli gene. Comparisons of the M. bovis EPP63 beta pilin protein sequence with other pilin gene sequences are presented.