Dichelobacter nodosus is the primary pathogen implicated in ovine foot
rot. In this paper we have delineated a 27 kb locus, termed the virule
nce-related locus (vrl), that was essentially specific for virulent D.
nodosus isolates. The precise ends of this locus were mapped and the
sequences of the junction regions from the virulent strain A198 were c
ompared to corresponding sequences from the benign isolate C305. The l
eft end of the vrl locus was located in a sequence similar to that of
the small stable 10Sa RNA molecule of Escherichia coil, next to a phag
e-attachment-site-like sequence, which indicated that the vrl locus mi
ght have arisen by the integration of a phage. However, no attachment-
like sequence could be found at the right end of the vrl locus. In the
chromosome of the benign strain the sequences bordering vrl were not
contiguous but were separated by about 3 kb. It was concluded that the
divergence of the benign and virulent strains at this locus was a mul
ti-step process. Several potential ORFs were identified at the junctio
n regions but only one ORF, encoding a 126 kDa protein, was expressed
in a T7 expression system in E. coil.