Molecular characterization of the TIA-1 like RNA binding protein of the silk worm, Bombyx mori.

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BmTRN-1 from the silkworm, Bombyx mori, is an RNA-binding protein homologous to mammalian TIA-1/TIAR, that possesses three RNA recognition motifs (RRMs) followed by a C-terminal auxiliary domain. Previous studies showed that the function of the BmTRN-1 is possibly involved in several mechanisms of RNA metabolism including the regulation of transcripts in the Bombyx cultured cells. In this study, the RRM2 and RRM1 domain of BmTRN-1 were found to be related to its nuclear export and nuclear accumulation, respectively. Also, Analyses by using the expressed GFP-BmTRN-1 fusion protein in the cells indicated that the BmTRN-1 distribution is drastically changed, and further indicated that the protein is distributed in the cytoplasm and forms aggregate structure, especially when the cells are infected by a baculovirus, Bombyx mori nucleopolyhedrovirus (BmNPV). Protein expression level of a BmNPV reporter protein was shown to be altered both by the BmTRN-1-overexpression and BmTRN-1-knockdown in the cultured cells and the transgenic individual tissues. In addition, we found that BmTRN-1 interacts with one of the BmNPV's nucleic acid-binding protein and the C-terminal auxiliary domain of BmTRN-1 is important for its interaction with the viral protein. Thus, it was indicated from these findings that the interaction between BmTRN-1 and the viral protein relates to the possible cellular function of resisting baculovirus proliferation.