Characterization of the TRBP domain required for dicer interaction and function in RNA interference

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Interference

Background:

• Dicer, Ago2, and TRBP are essential for human RNA-induced silencing complex (RISC) assembly.
• TRBP, a double-stranded RNA binding protein (dsRBP), facilitates small interfering RNA loading into RISC and directly binds Dicer via its C-terminal domain.

Purpose of the Study:

• To identify and characterize the specific domains responsible for the interaction between TRBP and Dicer.
• To determine the functional significance of the TRBP-Dicer interaction in RNA interference (RNAi).

Main Methods:

• Co-immunoprecipitation assays to assess TRBP-Dicer binding.
• Site-directed mutagenesis to create TRBP variants lacking the C4 domain (TRBPsΔC4).
• Immunofluorescence microscopy to evaluate TRBP and Dicer colocalization.
• RNA interference rescue experiments in TRBP-deficient cells.

Main Results:

• A 165 amino acid region in Dicer and a 69 amino acid C-terminal domain (C4) in TRBP were identified as the interaction sites.
• TRBP isoforms containing the C4 domain (TRBP1, TRBP2) co-immunoprecipitated with Dicer, while TRBPsΔC4 did not.
• Full-length TRBPs colocalized with Dicer, but TRBPsΔC4 did not, indicating the C4 domain is crucial for Dicer binding and colocalization.
• TRBP1 and TRBP2, but not TRBPsΔC4, rescued RNAi function in tarbp2-/- cells and in human cells with compromised RNAi activity.

Conclusions:

• The C4 domain of TRBP is necessary for direct binding and colocalization with Dicer.
• TRBP and Dicer interaction is independent of bound double-stranded RNA.
• TRBP binding to Dicer is critical for efficient RNA interference pathway function.