Ers1, a Rapidly Diverging Protein Essential for RNA Interference-dependent Heterochromatic Silencing in Schizosaccharomyces pombe

Mathieu Rougemaille,Smita Shankar,Sigurd Braun,Margot Rowley,Hiten D Madhani

doi:10.1074/jbc.c800140200

Mathieu Rougemaille, Smita Shankar + Show 3 more

Open Access

https://doi.org/10.1074/jbc.c800140200

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Abstract

Centromeric silencing and heterochromatin formation in Schizosaccharomyces pombe require the RNA interference (RNAi) machinery. Three factors that mediate this mechanism have been identified: 1) the RNA-dependent RNA polymerase complex RdRC, 2) the Argonaute-containing RITS (RNA-induced initiation of transcriptional silencing) complex, and 3) the endoribonuclease Dicer ortholog Dcr1. S. pombe mutants lacking a new factor described here, Ers1, are completely defective in RNAi-dependent silencing of centromeric regions but, importantly, not in RNAi-independent silencing at the mat3M or tel2R loci. ers1Delta cells likewise fail to convert centromeric pre-small interfering RNA transcripts into small interfering RNAs, are defective in histone H3 Lys(9) methylation, and are unable to recruit the RITS complex to centromeric sequences. Surprisingly, Ers1 lacks obvious orthologs outside of the genus Schizosaccharomyces. Within this group, it is diverging rapidly, raising the possibility that it is coevolving with target RNA elements.

Highlights

Heterochromatin formation and gene silencing in many eukaryotes require a core system of a histone H3 Lys9 (H3-K9) methyltransferase and a family of proteins that recognize this modification
To identify new factors required for RNAi-dependent heterochromatin formation, we sought to generate and test knockout mutants of genes coding for proteins that localize to heterochromatin
To enrich for such factors, we took advantage of work that determined the subcellular localization of yellow fluorescent protein fusions for most S. pombe open reading frames [8]

Summary

Introduction

Heterochromatin formation and gene silencing in many eukaryotes require a core system of a histone H3 Lys9 (H3-K9) methyltransferase and a family of proteins (the HP1 family) that recognize this modification. No factors essential for and specific to RNAi-dependent heterochromatin formation in S. pombe have been reported besides those polypeptides identified in the RITS and RdRC complexes. ACCELERATED PUBLICATION: Ers1 Mediates Centromeric Silencing slurry of protein A-Sepharose washed with lysis buffer was added to the antibody incubations and agitated on a Nutator for 3 h.

Results

Conclusion