Eri1: a conserved enzyme at the crossroads of multiple RNA-processing pathways

• Eri1 processes ribosomal RNA, histone mRNA, and small regulatory RNAs.
• Eri1 exemplifies a growing class of multifunctional small RNA-processing proteins.
• Eri1 has been evolutionarily recruited into diverse small regulatory RNA pathways.
• Eri1 may coordinate the activity of diverse cellular processes regulated by RNA.

Eri1 is an evolutionarily conserved 3′–5′ exoribonuclease that participates in 5.8S rRNA 3′ end processing and turnover of replication-dependent histone mRNAs. Over the course of evolution, Eri1 has also been recruited into a variety of conserved and species-specific regulatory small RNA pathways that include endogenous small interfering (si)RNAs and miRNAs. Recent advances in Eri1 biology illustrate the importance of RNA metabolism in epigenetic gene regulation and illuminate common principles and players in RNA biogenesis and turnover. In this review, we highlight Eri1 as a member of a growing class of ribosome- and histone mRNA-associated proteins that have been recruited into divergent RNA metabolic pathways. We summarize recent advances in the understanding of Eri1 function in these pathways and discuss how Eri1 impacts gene expression and physiology in a variety of eukaryotic species. This emerging view highlights the possibility for crosstalk and coregulation of diverse cellular processes regulated by RNA.