Analysis of similarity of the SI gene in infectious bronchitis virus (IBV) isolates in Shanghai, China

Abstract

The aim of the study was to analyze the similarity of the SI gene in 5 novel viral strains of infectious bronchitis virus (IBV) isolated in Shanghai, China, using a pair of specific primers which were designed based on the published sequences of the S gene of IBV. The 5 full-length cDNA segments of the SI gene were amplified from the 5 isolated strains with RT-PCR. It was confirmed that the nucleotide sequences of the SI gene in the 5 strains isolated from chickens and pigeon have a length of 1626 bp and encode 541 amino acid residues. Compared to the sequence of selected reference IBV strains published in GenBank, the 4 strains from chickens exhibited 77.4%-82.9% identity in the SI gene sequence, with the deduced similarity of the protein sequence being 74.7%-82.6%, while the strain from pigeon exhibited 79.3%-99.6% similarity in the SI gene sequence, with a deduced identity of the protein sequence of 81.6%-99.6%. The SI protein cleavage site sequence of these isolates contains 5 consecutive basic amino acids, named, Arg-Arg-Phe-Arg-Arg (RRFRR) similar to most of IBV strains. The results indicated that the variability range of the SI gene structure is high, corresponding with the biological character of IBV, and that molecularly the five isolated strains from Shanghai have a close relationship with the IBV reference strains. It was concluded that the five isolated strains belong to IBV, even though one of them was isolated from pigeons.