Molecular Basis for poly(A) RNP Architecture and Recognition by the Pan2-Pan3 Deadenylase

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Eukaryotic mRNA stability is governed by a ribonucleoprotein (RNP) complex involving poly(A)-binding proteins (PABPC1/Pab1) on the poly(A) tail.
• This poly(A) RNP complex protects mRNAs from degradation and activates the Pan2-Pan3 deadenylase for poly(A) tail shortening.

Purpose of the Study:

• To elucidate the mechanism by which the Pan2-Pan3 deadenylase complex interacts with and degrades poly(A) RNPs.
• To determine the structural basis for poly(A) tail length regulation by Pab1 oligomers.

Main Methods:

• Reconstitution of the poly(A) RNP and Pan2-Pan3 deadenylase complex in vitro using recombinant proteins.
• Cryo-electron microscopy (cryo-EM) to determine the structure of the complex.
• Biochemical assays to analyze deadenylase activity.

Main Results:

• Pan2-Pan3 deadenylase associates with and degrades poly(A) RNPs containing at least two Pab1 molecules.
• The cryo-EM structure reveals how Pab1 oligomerization interfaces are recognized by Pan2-Pan3, threading the poly(A) RNA into the active site.
• The structure explains the periodic architecture observed at the 3' end of cytoplasmic mRNAs.

Conclusions:

• Pab1 oligomers on the poly(A) tail act as molecular rulers, controlling the rate of deadenylation.
• This mechanism provides mechanistic insight into how mRNA poly(A) tail length is regulated throughout the mRNA's lifespan.
• The findings illuminate the structural basis for mRNA decay regulation.