The p10 gene of Bombyx mori nucleopolyhedrosis virus encodes a 7.5-kDa protein and is hypertranscribed from a TAAG motif

In baculovirus-based high-level expression of cloned foreign genes, the vir al very late gene promoters of polyhedrin (polh) and p10 are extensively ex ploited. Here we report the cloning and characterization of the p10 gene fr om a local isolate of Bombyx mori nucleopolyhedrosis virus (BmNPV). The gen e harbours a 213-bp open reading frame encoding a protein of 70 amino acids with a predicted molecular mass of 7.5 kDa. The BmNPV p10 showed deletion of a single A at +210 nucleotide compared to the prototype baculovirus, Aut ographa californica multinucleocapsid nucleopolyhedrosis virus (AcMNPV), p1 0 gent, resulting in a translational frameshift to generate a termination c odon and consequently a truncated polypeptide instead of the 10-kDa protein . This protein P7.5 from BmNPV has a putative leucine zipper dimerization m otif towards the N-terminal end and the central nuclear disintegration doma in but the carboxy-terminal domain implicated in protein association for fi brillar structure formation is absent. Phylogenetic analysis revealed that p10 is highly conserved among baculoviruses and the BmNPV strains are more closely related to AcMNPV than other baculoviruses. The transcription of p1 0 is regulated in a temporal manner. reaching maximal levels by 72 h post-i nfection. RNAase protection and primer extension analysis mapped the transc ription start sites at -70 and -71 nt with respect to the ATG, within the c onserved baculovirus late gene motif TAAG. The upstream region showed compl ete homology to the strong promoter of the AcMNPV p10. suggesting that this promoter from BmNPV could also be exploited for high-level expression of c loned Foreign genes in silkworm cells or larvae.