A new yeast poly(A) polymerase complex involved in RNA quality control

Area of Science:

• Molecular Biology
• RNA Metabolism
• Cellular Quality Control

Background:

• Eukaryotic cells possess multiple poly(A) polymerases beyond those for mRNA.
• Trf4p in yeast is linked to quality control, involving polyadenylation and degradation of hypomethylated initiator tRNA (tRNAiMet).

Purpose of the Study:

• To characterize the Trf4p-containing poly(A) polymerase complex.
• To investigate the role of this complex in RNA quality control and degradation.

Main Methods:

• Affinity purification of Trf4 complex from yeast.
• Reconstitution of the complex from recombinant components.
• In vitro polyadenylation assays with native and in vitro transcribed tRNAs.
• Exosome-mediated degradation assays using nuclear exosome fractions.

Main Results:

• Trf4p is the catalytic subunit of a novel poly(A) polymerase complex including Air1p/Air2p and Mtr4p.
• The Trf4 complex preferentially polyadenylates unmodified, in vitro transcribed tRNAiMet over native tRNAiMet.
• The complex distinguishes between correctly and incorrectly folded tRNAs.
• Polyadenylation by the Trf4 complex enhances exosome-dependent degradation of tRNAiMet, with poly(A) tails acting as exosome recruitment signals.

Conclusions:

• The Trf4 complex functions in RNA surveillance by polyadenylating and targeting aberrant RNAs for degradation.
• This mechanism, involving poly(A) tail-mediated exosome recruitment, is crucial for maintaining RNA quality in eukaryotic cells.
• The findings reveal a conserved RNA turnover strategy similar to that observed in bacteria.