Sequence analysis of cDNA gene coding for VP2 of CJ801 strain of infectious bursal disease virus

Abstract

A cDNA fragment with a length of 1500bp coding for VP2 of infectious bursal disease virus (IBDV) has been amplified by reverse transcription-polymerase chain reaction(RT-PCR)from CJ 801 strain isolated in China. DNA sequence analysis showed that the similarities of nucleotide sequence of CJ801 strain with classical type I strains 52/70, STC and Cul were 97.4%, 97.6% and 96.9% respectively, those with variant strains A, E and GLS were a little smaller, 96.5%, 96.3% and 96.9%,respectively, and those with type Ⅱ strains were about 81%. Cluster analysis of nucleotide sequences indicated that CJ801 strain is more closely related to classical virulent strains and classical tissue culture-adapted strains than to variant strains, very virulent strains and type Ⅱ strains. Comparison of deduced amino acid sequences showed that the homogenneities of CJ 801 strain with all classical type I strains were over 96%.The most closely related strain to CJ801 strain is 52/70 strain, in which the divergence of amino acid sequences was only 1.8%. A serine-rich heptapeptide(S-W-S-A-S-G-S),which is a signature of virulent IBDV strains, is also present in CJ801, indicating that CJ801 is a classical virulent IBDV strain.At positions 253,279 and 284,the amino acid residues of CJ801 strain are Q, D and A respectively, conserved in that of virulent strains . However, in the attenuated strain of CJ801 (CJ801 BKF),the residues at these positions were substituted by H,N and T respectively.There substitutions were commonly found in cell culture adapted IBDV strains. It is suggested that these amino acid residues, 253 Q,279 D and 284 A can be regarded as signature of virulent strains of IBDV in addition to the serine rich heptapeptide.