Evidence of genetic diversity generated by recombination among avian coronavirus IBV.

Previously, we demonstrated that the DE072 strain of IBV is a recombinant which has an IBV strain D1466-like sequence in the S gene. Herein, we analyzed the remaining 3.8 kb 3' end of the genome, which includes Gene 3, Gene 4, Gene 5, Gene 6, and the 3' non-coding region of the DE072 and D1466 strains. Those two viruses had high nucleotide similarity in Gene 4. However, the other individual genes had a much different level of sequence similarity with the same gene of the other IBV strains. The genome of five IBV strains, of which the complete sequence of the 3' end of the genome has been determined, were divided at an intergenic (IG) consensus sequence (CTGAACAA or CTTAACAA) and compared phylogenetically. Phylogenetic trees of different topology indicated that the consensus IG sequences and the highly conserved sequence around this regions may serve as recombination 'hot spots'. Phylogenetic analysis of selected regions of the genome of the DE072 serotype field isolates further support those results and indicate that isolates within the same serotype may have different amounts of nucleotide sequence similarity with each other in individual genes other than the S gene. Presumably this occurs because the consensus IG sequence serves as the template switching site for the viral encoded polymerase.