Genetic Variance Analysis of Nucleocapsid Protein Gene of Infectious Bronchitis Viruses with Different Tissue Tropism
Two specific primers were designed according to the published sequence of nucleocapsid(N)protein gene of strain Beaudette of infectious bronchitis virus(IBV)from GenBank.cDNA of N gene was amplified by reverse transcription polymerase chain reaction(RT-PCR)from viral RNAs of proventriculopathogenic IBV strain ZJ971,nephropathogenic IBV strains N,X and IBV vaccine strain H52 respectively.They were cloned into vector pBluescript SK(+) and sequenced by the dideoxy-mediated chain termination method.The results indicated that the complete open reading frame(ORF)of N gene is 1230bp in length,which encodes a protein of 409 amino acids.Compared with N gene of the other 8 IBV strains from GenBank,the homology of nucleotide and deduced amino acid sequences was 88.2%-98.6% and 91.2%-97.8% for ZJ971,86.6%-87.4% and 90.5%-91.5% for N,86.3%-87.4% and 90.0%-91.5% for X,90.4%-98.3% and 92.0%-98.0% for H52 respectively.The characteristics of variation of N gene for ZJ971,X and N strains was scattered point mutation without obvious HVR, while those of X and N tend to vary in middle and rear regions relatively.These findings showed that variation of nucleocapsid protein gene of IBV with different tissue tropism was different.Variation of amino acid sequence of nucleocapsid protein of proventriculopathogenic IBV strain ZJ971 was characterized with H 111D,S 117A,V 142L,P 171A,E 401D;and that of nephropathogenic IBV strains N and X was characterized with A 46S?A 48P?L 189R?N 190S?E 220D?I 223A?V 236Y?S 237K?K 240Q?Q 286R?T 299K?R 301E?E 334D?V 335E?V 336P and T 351S.