Molecular characterization of the RNA-binding protein, TRN-1 in the lepidopteran insects

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TRN-1, an RNA-binding protein homologous with mammalian T-cell intracellular antigen-1 has been found to express in every tissue of the Iepidopteran, Bombyx mori and Spodoptera frugiperda. TRN-1 molecule has been shown to possess the domain structure consisting of three-repetitive potential RNA-recognition motifs (RRMs) in the N-terminal followed by auxiliary domain in the C-terminal as similar with TIA-1 family, and to function as a modulator protein for transcripts by investigating the production of foreign recombinant proteins and transcripts in the Bombyx TRN-1 knock-down BmN4 cells (Kotani, et. al., Gene 320, 67-79, 2003). Subcellular localization and role of each domain of the Bombyx TRN-1 in the cultured cells has been investigated by the confocal fluorescence microscopy analyses on the cells over-expressing GFP-TRN-1 fusion protein and GFP-TRN-1 lacking C-terminal auxiliary domain and RRM domain in order to gain more insight into cellular function of the TRN-1. The recombinant GFP-fusion proteins with RRMs were indicated to assuredly have the poly (U) RNA binding activity. It was also shown that GFP-TRN-1 lacking C-terminal auxiliary domain and GFP-C-terminal domain were likely to be localized in the nucleus, while full-length GFP-TRN-1 was localized both in the nucleus and cytoplasm. However, clear localization of GFP-TRN-1 in the nucleus was observed after AcNPV was infected into the cells. In addition, it was indicated that GFP-TRN-1 over-expression could cause change of the recombinant baculovirus-produced luciferase activity during its infection, thus demonstrating that lepidopteran TRN-1 may control the function of both baculovirus and cellular transcripts in the response to stress caused by the viral infection.