A conserved ncRNA-binding protein recruits silencing factors to heterochromatin through an RNAi-independent mechanism

Abstract

Long noncoding RNAs (lncRNAs) can trigger repressive chromatin, but how they recruit silencing factors remains unclear. In Schizosaccharomyces pombe, heterochromatin assembly on transcribed noncoding pericentromeric repeats requires both RNAi and RNAi-independent mechanisms. In Saccharomyces cerevisiae, which lacks a repressive chromatin mark (H3K9me [methylated Lys9 on histone H3]), unstable ncRNAs are recognized by the RNA-binding protein Nrd1. We show that the S. pombe ortholog Seb1 is associated with pericentromeric lncRNAs. Individual mutation of dcr1⁺ (Dicer) or seb1⁺ results in equivalent partial reductions of pericentromeric H3K9me levels, but a double mutation eliminates this mark. Seb1 functions independently of RNAi by recruiting the NuRD (nucleosome remodeling and deacetylase)-related chromatin-modifying complex SHREC (Snf2–HDAC [histone deacetylase] repressor complex).