ATP-independent diffusion of double-stranded RNA binding proteins

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• Proteins with double-stranded RNA binding domains (dsRBDs) perform crucial roles in RNA processing, including localization, splicing, editing, export, and translation.
• The precise mechanisms and functional importance of dsRBDs are not fully understood.
• Transactivation response RNA binding protein (TRBP) is a key protein with three dsRBDs involved in HIV replication, immune responses via protein kinase R (PKR), and RNA silencing.

Purpose of the Study:

• To investigate the mechanistic basis and functional significance of dsRBDs, focusing on the diffusion activity of TRBP on dsRNA.
• To determine the role of individual dsRBDs within TRBP in this diffusion process.
• To explore if this diffusion activity is conserved among TRBP homologs and its impact on Dicer-mediated RNA processing.

Main Methods:

• Investigated the diffusion activity of TRBP on dsRNA using biophysical techniques.
• Performed deletion analyses to identify the essential dsRBDs for TRBP diffusion.
• Examined the diffusion of TRBP homologs (PKR activator, R3D1-L) on dsRNA.
• Studied the diffusion dynamics of a Dicer-TRBP complex on dsRNA and correlated it with Dicer's catalytic activity.

Main Results:

• TRBP demonstrates ATP-independent diffusion exclusively on dsRNA in a length-dependent manner.
• The first two dsRBDs of TRBP are critical for its dsRNA diffusion activity, while the third dsRBD is dispensable.
• TRBP homologs, PKR activator and R3D1-L, exhibit similar dsRNA diffusion, suggesting a conserved family trait.
• A Dicer-TRBP complex displays dynamic diffusion on dsRNA, which correlates with Dicer's catalytic efficiency.

Conclusions:

• TRBP possesses a unique dsRNA-specific diffusion activity mediated by its N-terminal dsRBDs.
• This dsRNA diffusion activity of TRBP is conserved across related proteins and plays a role in enhancing siRNA and miRNA processing by Dicer.
• The findings provide mechanistic insights into how dsRBD-containing proteins interact with dsRNA to regulate gene expression and cellular processes.