Very virulent infectious bursal disease virus(vvIBDV)was isolated from chicken bursa and then the virus double stranded RNA was extracted After denaturation of dsRNA by heat in the presence of primers,the cDNA was synthesized by use of a reverse transcriptase lacking RNase H activity The RNA component of RNA cDNA hybrids was digested by RNase H By using an optimized PCR,a 3 05kb DNA fragment coding for precursor polyprotein of IBDV was produced in one step,which was inserted into pcDNA3 1(+) vector Two recombinant plasmids (pPP1 and pPP2)were screened and identified from eight XL1 blue colonies Partial sequencing for pPP1 plasmid indicated that the precursor polyprotein gene for IBDV was cloned successfully The method can simplify greatly the procedure to clone precursor polyprotein gene of IBDV
