Identification of nonviral infection-specific polypeptides in the midgut of the silkworm, Bombyx mori, infected with B. mori densovirus type 2

摘要

Two unique polypeptides with apparent molecular weights (MWs) of 45,500 (45.5K) and 44K were identified in the purified BmDNV-2 preparation from the pupal midgut of the silkworm, Bombyx mori, that had previously been infected with B. mori densovirustype 2 (BmDNV-2) at a larval stage. Immunoblot analysis and peptide mapping showed that both 45.5K and 44K polypeptides were serologically and structurally distinct from the structural polypeptides of BmDNV-2, suggesting that these two polypeptides werenot minted to the polypeptides for virion structure. Comparison of directly determined NH_2-terminal amino acid sequences of 45.5K and 44K polypeptides with those deduced from the nucleotide sequences of BmDNV-2 genomic DNAs implied that they were not coded by viral genome. Based on the fact that 45.5K and 44K polypeptides were related serologically and structurally but distinct in their NH_2-terminal amino acid sequences, 45.5K polypeptide seemed to contain entire or nearly entire amino acid sequenceof 44K polypeptide and a unique NH_2-terminal amino acid extension. The 45.5K and 44K polypeptides were found only in the midgut of BmDNV-2-infected silkworm, and were not detected in fat body, Malpighian tubule, ovary and hemotymph of the same infectedinsects. In the BmDNV-2-infected midgut, conspicuous accumulation of these two polypeptides is achieved only at two specific times, one being 2-3 days postinoculation and the other at larval-pupal transformation onward. These results suggest that 45.5K and 44K polypeptides are involved in the degeneration and discharge of virus-infected midgut cells.