A LIN28-dependent structural change in pre-let-7g directly inhibits dicer processing

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• LIN28 is a cytoplasmic RNA-binding protein known to inhibit let-7 microRNA biogenesis.
• The precise mechanism by which LIN28 inhibits let-7 microRNA processing, particularly at the Dicer step, remains unclear.

Purpose of the Study:

• To investigate the molecular basis and function of the interaction between LIN28 and the let-7g precursor (pre-let-7g).
• To elucidate the mechanism by which LIN28 inhibits let-7g biogenesis at the Dicer processing stage.

Main Methods:

• In vitro study combining RNase footprinting, gel shift binding assays, and processing assays.
• Structural mapping of pre-let-7g and identification of LIN28 interaction sites.
• Analysis of conformational changes in pre-let-7g upon LIN28 binding.

Main Results:

• Identified specific regions in the terminal loop of pre-let-7g that physically interact with LIN28.
• Demonstrated that LIN28 binding induces a conformational change, unwinding a double-stranded region crucial for Dicer processing.
• Showed that a pre-let-7g mutant with an open upper stem mimicked LIN28's inhibitory effect on Dicer processing.

Conclusions:

• LIN28 directly inhibits let-7g biogenesis by interfering with Dicer processing.
• The mechanism involves LIN28 binding to pre-let-7g, causing structural changes that block enzyme access.
• This study provides a detailed molecular understanding of LIN28-mediated microRNA regulation.