grown in grace medium grace 1962 supplemented with 10 foetal calf serum plus antibiotics for immunological assays like rip or ipma and for protein production sf21 cells were grown in sf900 serum free medium gibco u2014 brl plus antibiotics in order to reduce the background of wild type virus modified acnpv in which the p10 gene was exchanged for a synthetic and unique bsu36i restriction site was used for cotransfection martens et al 1994 after homologous recombination between wild type virus and the transfer vector circular recombinant viral dna will be formed which can infect sf21 cells non circular dna is not infectious and therefore background will be reduced however due to non homologous recombination background percentage will be reduced from 95 to 70 only martens 1994 restriction enzymes and phage t4 dna ligase were purchased from biolabs usa and used as recommended by the supplier 35 s methionine was obtained from amersham uk venr u2122 dna polymerase was from biolabs usa all cloning procedures were carried out essentially according to sambrook et al 1989 the cdna coding for bfsha was purified after double digestion of the plasmid bov alpha psp64 1 leung et al 1987 with nco i plus xba i the dna of 554 bp 39 s contained a signal sequence of 72 bp at the 5 u2032 end and an untranslated region of 188 bp at the.