Gene families encoding phase- and size-variable surface lipoproteins of Mycoplasma hyorhinis

A prototype family of seven genes encoding the variable surface lipoprotein s (Vlps) of Mycoplasma hyorhinis is characterized in the pathogenic SK76 st rain, using long-range PCR to amplify and analyze the single chromosomal re gion containing expressed genes vlpA to -G, each of which is subject to pha se and size variation. Smaller families of vlp genes in subclones of SK76 o r in another strain of M.. hyorhinis, GDL, can be attributed to deletions o f specific vip genes from the prototype array described here. Two genes, vl pA and the newly revealed vlpG, contain repeat motifs in their 3' coding re gions that differ from the short tandem repeats in other vlp genes Set reta in structural features common to all rip gene products. SK76 and GDL vip ge ne families are similarly organized and show sequence similarity between co rresponding individual Flp genes. In light of the extensive potential for d iversity within the rip gene system, such conservation provides a provision al basis to hypothesize that pip genes may exist in specific arrays that en dow selected functions while retaining common structural features required during phase-variable expression of this set of gene products.