Comparison of the rompA gene repeat regions of Rickettsiae reveals species-specific arrangements of individual repeating units.

Genes containing repeating units have been described for several eukaryotic and prokaryotic proteins, although none exhibit the extraordinary length and conservation seen with the Rickettsia rickettsii 190-kDa protein (OmpA) repeat region. The genetic organization of the repeat regions of the ompA gene for R. conorii and R. akari was examined and compared to that of R. rickettsii. Individual repeating units, which constitute the makeup of the repeat regions, share extensive DNA homology among these species. However, differences were observed in the overall numbers and arrangements of repeating units within each species' repeat region. It appears that the distinctive arrangement of repeating units within the gene may represent the basis for encoding a protective species-specific conformational epitope of the protein.