ANALYSIS OF A HYPERVARIABLE REGION IN THE 3' NONCODING END OF THE INFECTIOUS-BRONCHITIS VIRUS GENOME

Previous studies on infectious bronchitis virus (IBV) cDNA have identi fied a region of about 184 bases in the 3' non-coding terminus of both the U.S. prototype strain (Beaudette) and a Japanese strain (KB8523), that was not present in an antigenically closely related U.S. strain, Massachusetts (Mass) 41 (Boursnell et al., 1985; Sutou et al., 1988). In order to investigate the origin and function of this region and it s occurrence in nature, the cDNA sequences of the 3' non-coding region s of three additional strains of IBV, Gray, Arkansas (Ark) 99 and Holl and (Holl) 52, were determined and compared to the sequences of the Be audette, KB8523 and Mass41 strains. Not only was this U-rich sequence absent from the 3' non-coding region of the Mass41 strain, it was also highly variable, especially in comparison to the highly conserved 3' non coding region downstream of this sequence. Computer analyses of th e sequences adjacent to this hypervariable region (HVR) showed that th e 3' end of the IBV genome was highly conserved downstream of this reg ion, with 94.3 to 97.8% similarity. However, the similarities for the HVR ranged from 53.2% between Holl52 and Ark99, to 92.8% between Beaud ette and Gray. The flanking sequences were not only conserved but thes e sequences upstream and downstream of the HVR also formed mirrored im ages.