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Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) strain H produces many hexahedral polyhedra (inclusion bodies) in the cytoplasm of insect midgut epithelial cells. The mutant A strain, however, produces polyhedra in the nucleus. We determined cDNA sequences of the polyhedrin genes, the smallest of the 10 genome segments, of these two strains. The polyhedrin genes of the H and A strains were 944 bp long, and encoded polypeptides of 248 amino acids (M r 28500) and 252 amino acids (M r 29000), respectively. The extra four amino acid residues at the carboxy terminus of the strain A polyhedrin (Arg-Leu-Leu-Val) were the result of a single nucleotide substitution at an opal stop codon (TGA → CGA). A further amino acid substitution of the histidine residue at position 101 (His → Tyr) was seen. The carboxy-terminal extension revealed a considerable similarity to the consensus amino acid sequence of the DNA-binding domain of many DNA-binding proteins. We discuss the relationship between the intracellular localization of polyhedrins and mutations in their amino acid sequences.
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