D. Yogev et al., INCREASED STRUCTURAL AND COMBINATORIAL DIVERSITY IN AN EXTENDED FAMILY OF GENES ENCODING VLP SURFACE-PROTEINS OF MYCOPLASMA-HYORHINIS, Journal of bacteriology, 177(19), 1995, pp. 5636-5643
Variable lipoproteins (Vlp) constitute the major coat protein of Mycop
lasma hyorhinis. They are products of multiple, divergent, single-copy
genes organized in a chromosomal cluster, Three genes, vlpA, vlpB, an
d vlpC, have been previously identified in clonal isolates of M. hyorh
inis SK76. Each is linked to a characteristic promoter region containi
ng a homopolymeric tract of adenine residues [poly(A) tract], subject
to hypermutation that transcriptionally controls phase variation of vi
p genes and leads to combinatorial surface mosaics of distinct Vlp pro
ducts, The size of the natural rip gene repertoire is unknown but may
critically determine the degree of structural and combinatorial divers
ity available in this species, In this study, the vip repertoire of M.
hyorhinis GDL-1 was characterized and shown to contain three addition
al genes, vlpD, vlpE, and vlpF, clustered with other known vlp genes i
n the order 5'-vlpD-vlpE-vlpF-IS-vlpA-IS-vlpB-vlpC-3' where IS represe
nts copies of the IS1221 element of M. hyorhinis. The 5' boundary of t
his expanded family was identical to that of the more limited family 5
'-vlpA-IS-vlpB-vlpC-3' previously described in a clonal isolate of str
ain SK76, A recombinant construct containing vlpD, vlpE, and vlpF expr
essed antigenically distinguishable products corresponding to each gen
e, These genes encode characteristic C-terminal repetitive regions tha
t are subject to size variation by insertion or deletion of intragenic
repeats but maintain an extended, charged structure, Each vip gene al
so contained characteristic alternative open reading frames, which pro
vide a potential reservoir of coding sequence for Vip diversity, possi
bly recruited through insertion and/or deletion mutations. These findi
ngs demonstrate a vastly expanded potential for structural diversity a
nd combinatorial display of surface mosaics on this organism and sugge
st that modulation of the vip repertoire, possibly in conjunction with
mobile elements, may determine the capacity for surface variation in
natural populations and laboratory strains of this mycoplasma species.