The genetic relatedness of a number of individual cognate genes of viruses in the bluetongue and closely related serogroups.

Genome segments 2, 4, 6, 7, 8, 9, and 10 of bluetongue virus (BTV) serotype 10 were cloned in pBR322. The 2926-bp S2 gene, which codes for the serotype-specific antigen, was cloned as two overlapping 2.4-kb inserts. The relatedness of cognate S2 genes among different isolates of BTV10 was investigated by hybridization, restriction enzyme mapping, and sequencing of the terminal ends. Hybridization under high stringency conditions indicated a genetic diversity between isolates of BTV10 from South Africa and the United States. This was confirmed by a comparison of the restriction map of the cloned S2 gene of a BTV10 isolate from South Africa to that of the S2 gene of the BTV10 strain of the United States which has been cloned and sequenced by Purdy et al. (1985). The part of the genome that was sequenced indicated, however, that this variation was confined to an approximately 10% sequence divergence in the coding region. Very few of the nucleotide substitutions resulted in an amino acid change. The genetic variation of cognate BTV genes within the BTV serogroup as well as among different members of closely related serogroups was also investigated. DNA probes from cloned BTV10 segments were hybridized to dsRNA from 24 different BTV serotypes. Genome segments S2 and S6 were found to be almost equally serotype specific. The stringency of the wash solutions after hybridization can be manipulated to determine an order of relatedness of different cognate genes. This was illustrated by the hybridization of a sensitive RNA probe of S7 to different BTV serotypes as well as to dsRNA from closely related orbiviruses. The results confirmed a relatedness between BTV and members of the epizootic hemorrhagic disease virus (EHDV) serogroups.