Genetic Relatedness of Colorado Tick Fever Virus Isolates by RNA-RNA Blot Hybridization

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Abstract
The sequence relatedness of ten isolates of the Colorado tick fever (CTF) serogroup of orbiviruses was examined by RNA-RNA blot hybridization. The 12 dsRNA genome segments of each of the isolates were electrophoresed in a 10% polyacrylamide gel, the segments were transferred electrophoretically to membranes and hybridized to radiolabelled genomic RNA from CTF Florio mouse-adapted strain (CTF FMA) or CTF SS-18. All genome segments of the ten CTF viruses exhibited cross-hybridization signals with either CTF FMA or CTF SS-18, under conditions in which .gtoreq. 74% sequence homology was required to form stable hybrids. Although the dsRNA polyacrylamide gel profiles were unique for each isolate examined, the CTF genes did not exhibit sequence divergence as has been seen among other Orbivirus serogroups. These hybridization analyses suggest that the CTF gene pool is relatively homogeneous which may be a reflection of the lack of multiple serotypes of CTF strains in neutralization tests. Nevertheless, the hybridization signals of segments 4 and 6 were lighter than those of the other genes, indicating that these two genes exhibited the highest degree of sequence variability among these isolates. These data are compared with hybridization data on other Orbivirus serogroups.