Analysis of the terminal sequences of the genome segments of four orbiviruses.
The RNA sequences of the terminal regions of the genome segments of 4 different orbiviruses were analysed. In 3 of these [bluetongue virus (BTV) types 1 and 20 and Ibaraki virus, a member of the epizootic hemorrhagic disease (EHD) serogroup], 1 strand of all of the genome segments analysed ends in 3'CAAUUU...5' while the other strand ends in 3'CAUUCA...5'. These conserved sequences are identical to those reported for BTV types 10 and 11. The 3' terminal sequences of segments 3 and 10 of the BTV 1 genome (including the conserved regions) were confirmed by the detection of exactly complementary sequences at the 5' termini of the ssRNA strands of opposite polarity. This also confirmed for these dsRNA segments (and by analogy for all of the genome segments of these viruses) that the dsRNA molecules are fully base-paired end to end. Using in vitro synthesised mRNA of BTV 1 in annealing experiments with the separated ssRNAs from the individual genome segments, it was shown that in each case the strand ending in 3'CAUUCA...5' is of the same polarity as the mRNA (+ve), while the strand ending in 3'CAAUUU...5' is of the opposite (-ve) polarity. The 4th virus analysed (Tilligerry, a member of the Eubenangee serogroup) only had 5 conserved bases at the 3' termini of 1 strand of each genome segment (3'CAU-CA...5') and 3 conserved bases at the 3' termini of the other strand (3'CA--U...5'). Considerable sequence homology was found in the near-terminal nonconserved regions of comparable genome segments, particularly between the different BTV types. There was little evidence however for absolute conservation of "segment specific" sequences in these regions of the RNA, as reported for rotaviruses. The percentage of sequence homology found in the terminal regions of the genome segments between members of the BTV, EHD and Eubenangee serogroups examined correlates with the serological interrelationships between these groups of viruses. The conserved terminal sequences and sequence homology in these regions of the RNA are discussed as to their role in virus replication and their significance to the reassortment of genome segments between different viruses during dual infections.
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D001483:Base Sequence; D001820:Bluetongue virus / Q000648:ultrastructure; D008970:Molecular Weight; D012330:RNA, Double-Stranded / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics*; D011995:Recombination, Genetic; D012087:Reoviridae / Q000235:genetics*; D013045:Species Specificity; D014779:Virus Replication
D012330:RNA, Double-Stranded; D012367:RNA, Viral