The resultant plasmid was designated as pLa-H5w. A cDNA of 1,746 nucleotides representing a BHG/QH/05 mutant HA gene in which the multiple basic amino acids at the cleavage site were deleted (36) was also inserted into the P-M intergenic region of pLa. The resultant plasmid was designated as pLa-H5m. Both pLa-H5w and pLa-H5m maintained NDV genome lengths that were a multiple of 6 to allow for efficient replication.