Extraction of mRNA from Stalled Ribosomes by the Ski Complex

The evolutionarily conserved Ski2-Ski3-Ski8 (Ski) complex containing the 3′→5′ RNA helicase Ski2 binds to 80S ribosomes near the mRNA entrance and facilitates 3′→5′ exosomal degradation of mRNA during ribosome-associated mRNA surveillance pathways. Here, we assayed Ski’s activity using an in vitro reconstituted translation system and report that this complex efficiently extracts mRNA from 80S ribosomes in the 3′→5′ direction in a nucleotide-by-nucleotide manner. The process is ATP dependent and can occur on pre- and post-translocation ribosomal complexes. The Ski complex can engage productively with mRNA and extract it from 80S complexes containing as few as 19 (but not 13) 3′-terminal mRNA nucleotides starting from the P site. The mRNA-extracting activity of the Ski complex suggests that its role in mRNA quality control pathways is not limited to acceleration of exosomal degradation and could include clearance of stalled ribosomes from mRNA, poising mRNA for degradation and rendering stalled ribosomes recyclable by Pelota/Hbs1/ABCE1. [Display omitted] •The evolutionarily conserved Ski complex extracts mRNA from 80S ribosomal complexes•mRNA extraction occurs in the 3′→5′ direction in a nucleotide-by-nucleotide manner•The process is ATP dependent and can occur on pre- and post-translocation ribosomes•19 mRNA nucleotides from the P site are sufficient for Ski-mediated mRNA extraction The evolutionarily conserved Ski complex containing the 3′→5′ RNA helicase Ski2 binds to 80S ribosomes near the mRNA entrance. Zinoviev et al. found that Ski extracts mRNA from 80S ribosomal complexes in the 3′→5′ direction in a nucleotide-by-nucleotide manner. Ski-mediated mRNA extraction renders ribosomal complexes susceptible to recycling by Pelota/Hbs1/ABCE1.