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ATP-independent diffusion of double-stranded RNA binding proteins

Koh, Hye Ran, Kidwell, Mary Anne, Ragunathan, Kaushik, Doudna, Jennifer A., Myong, Sua
Proceedings of the National Academy of Sciences of the United States of America 2013 v.110 no.1 pp. 151-156
Human immunodeficiency virus, RNA interference, RNA-binding proteins, catalytic activity, double-stranded RNA, exports, immune response, microRNA, small interfering RNA, transcriptional activation, translation (genetics)
The proteins harboring double-stranded RNA binding domains (dsRBDs) play diverse functional roles such as RNA localization, splicing, editing, export, and translation, yet mechanistic basis and functional significance of dsRBDs remain unclear. To unravel this enigma, we investigated transactivation response RNA binding protein (TRBP) consisting of three dsRBDs, which functions in HIV replication, protein kinase R(PKR)–mediated immune response, and RNA silencing. Here we report an ATP-independent diffusion activity of TRBP exclusively on dsRNA in a length-dependent manner. The first two dsRBDs of TRBP are essential for diffusion, whereas the third dsRBD is dispensable. Two homologs of TRBP, PKR activator and R3D1-L, displayed the same diffusion, implying a universality of the diffusion activity among this protein family. Furthermore, a Dicer–TRBP complex on dsRNA exhibited dynamic diffusion, which was correlated with Dicer’s catalytic activity. These results implicate the dsRNA-specific diffusion activity of TRBP that contributes to enhancing siRNA and miRNA processing by Dicer.