Sequence characterization of two new members of a multi-gene family in Serpulina hyodysenteriae (B204) with homology to a 39 kDa surface exposed protein: vspC and D.

Previous cloning and sequencing of clones from a genomic library constructed from Serpulina hyodysenteriae B204 had identified a tandem pair of open reading frames, identified as vspA and vspB (variable surface protein) expected to encode proteins with homology to ( but not identical with) a 39 kDa surface exposed membrane protein from this animal pathogen. Additional screening of the genomic library was performed to retrieve the remainder of the vspB gene using new oligonucleotide probes based upon the cloned gene sequences. Not only was this goal met but we also discovered two more adjacent and related vsp genes (vspC and vspD) and have completely sequenced them. They are all in a parallel orientation and appear to have a set of similar but distinct regulatory elements that may control separate expression of their open reading frames (ORFs). Thus, there are four contiguous vsp genes which are predicted to encode a family of structurally conserved proteins. The four adjacent open reading frames (ORFs) are of similar size (384-389 codons) and share from 83% to 90% identity in their amino acid sequence. Preliminary data suggests there may be yet another homologous gene copy in a distal location of S. hyodysenteriae that faithfully encodes the 39 kDa surface protein. The organization and homologies of these highly conserved multiple gene copies are discussed.