راحله مجدانی

Infectious bronchitis virus (IBV) is a pathogen causes acute and highly contagious disease infectious bronchitis (IB) in domestic chickens. The virus belongs to group III of genus Coronavirus in the family of Coronaviridae. It has an unsegmented, positive sense, single-stranded RNA (ssRNA) genome of approximately 27.6 kb in length and contains at least 10 open reading frames (ORFs) included: 5 -1a-1b-S (S1, S2)-3a-3b-3c (E)-M-5a-5b-N-Poly (A)-3. Gene 5, encoding two accessory proteins 5a and 5b, has been explained as important factor in pathogenesis of the virus .In this study the nucleotide sequences of Open Reading Frame (ORF) 5b of gene 5 of different IBV reference strains were obtained from Gene Bank and molecular properties of the strains were analyzed using bioinformatics softwares,Bioedite and MEGA7. Based on 5b nucleotide analysis, the rate of similarity among different strains of IBV was 86%-100%. Some strains from distinct geographical regions also had 100% similarity. The lowest similarity was observed between Australian strains with other IBVs (86%-95%). Based on the results of phylogenetic tree of gene 5b, Australian strains grouped together in a distinct cluster while other regions IBVs were classified differently regardless to their originated regions. High rate of similarity between different strains from distinct geoghrafical regions, could be confirm the important role for gene 5b in virus vital functions.