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.