Sequencing of the putative DNA helicase-encoding gene of the Bombyx mori nuclear polyhedrosis virus and fine-mapping of a region involved in host range expansion.

The complete sequence of a 3666-nucleotide (nt) open reading frame (ORF) and its flanking regions (58.1-62.1 map units (m.u.) from Bombyx mori nuclear polyhedrosis virus (BmNPV)) was determined. This ORF, BmNPV dnahel, encoded a predicted protein of 143623 Da which possessed seven consensus motifs found in proteins which unwind duplex DNAs, indicating that it is a DNA helicase. A 572-bp SacI-HindIII fragment, BmScH, that was previously shown to expand the host range of Autographa californica NPV (AcNPV) following homologous recombination [Maeda et al. (1993) J. Virol. 67, 6234-6238], was localized within BmNPV dnahel. By cotransfection experiments, two adjacent nt (A and T) that appeared to be the minimal essential sequence necessary to expand the host range of AcNPV, were mapped within BmScH. These adjacent nt encoded a single amino acid difference between BmNPV (Asp) and AcNPV (Ser).