Genetic Variations of Nucleocapsid Gene of Infectious Bronchitis Virus Strains Isolated in China during 1995-1999
Nucleocapsid protein(N protein) genes of ten IBV strains isolated in China between 1995 and 1999 were amplified by reverse transcriptase-polymerase chain reaction(RT-PCR),and then were cloned,sequenced and compared with 20 IBV reference strains.The results showed that all of the n genes of the ten isolates were composed of 1230 nucleotides,encoding a polypeptide of 409 amino acid residues.Deletion and insertion were not found in the n genes of the ten isolates.Phylogenetic tree based on amino acid sequences of n genes from ten IBV isolates and 20 reference IBV strains showed that the ten isolates were classified into three distinct clusters.IBV strains in the three clusters were isolated mainly in China.Furthermore,the phylogenetic tree also showed that recombination within the genome of IBV isolates may induce gene mutation of some Chinese IBV isolates.In addition,compared with the H120 vaccine strain,it was found that point mutations inducing the amino acid substitutions were common in n genes of the ten isolates. Taken together,these results suggested that gene mutation and recombination within the IBV genome existed in the Chinese IBV strains isolated between 1995 and 1999.