Sequence Analysis Of The Genome Of IBV Vaccine Strain H120

Infectious bronchitis virus(IBV) is a world-wide viral disease of poultry, which poses a major economic threat to the poultry industry. Because of relatively high variation of IBV, new variant strains continue to emerge. The cross-protection between different strain is weak. In spite of routine vaccination, the outbreaks of IB have been reported with high frequency. The strain H120 of Infectious Bronchitis Virus (IBV) is one of the earliest and representative attenuated live Infectious Bronchitis (IB) vaccine strains. To investigate the genomic feature of H120 and further identify weather it plays a role in the epidemiology of IBV, complete genome of H120 was sequenced and compared with genome sequences of other strains through phylogenetic and similarity plot analysis.18 pair primers were designed according to the complete genome sequences of IBV strains published on GenBank. The complete genome of H120 was found to consist of 27,631 nucleotides with a genomic structure similar to the strain of Beaudette. The gene 1 consists of two open reading frames (ORFs), ORF 1a and 1b, which are 11,802 and 8064 nt long respectively. Gene 2 is 3549 bases long, with a single ORF of 3489 nt. The S1 and S2 genes are 1596 and 1893 nt long each, and the overlap between the 3'end of ORF1b and the 5'end of the S protein gene is 110 nt long. Gene 3 consists of 709 nt, which contains three ORFs:3a,3b, and 3c (E protein gene). The ORFs consist of 174,195, and 330 nt, respectively. A total of 32 nt of the S protein gene overlap gene 3. Gene 4 (M protein gene) consists of 763 nt with a single ORF of 678 nt. Gene 5 contains two ORFs:5a and 5b with 198 and 249 nt, respectively.159 nt of 3'end of the 5b ORF overlap the 5'end of gene 6 (N protein gene). The N protein gene is 1331 bases long, with a single ORF of 1230 nt.Alignment analysis indicated that H120 exhibits highest similarity to ZJ971 with genomic identity rate of 99.8% and is least like most of the Chinese strains with 84.6-87.7% identity. In phylogenetic analysis, although different regions of H120 genome exhibited different topologies, H120 has a closer relationship with a non-Massachusetts serotype strain ArkDPI in phylogenetic tree of complete sequence. This study enriched the database of IBV biological information, has significance in further research on IBV genome function, prevalence and evolution.