Snf2 Family Protein Fft3 Suppresses Nucleosome Turnover to Promote Epigenetic Inheritance of Heterochromatin and Proper Replication of the Genome [BrdU IP]

BrdU profiling of replication activity in hydroxyurea treated synchronous culture of fission yeast. Heterochromatin can be epigenetically inherited in cis, leading to stable maintenance of gene expression states. However, the mechanisms underlying heterochromatin inheritance remain unclear. Here we identify Fft3, a homolog of the mammalian SMARCAD1 Snf2 chromatin remodeler, as a factor uniquely required for heterochromatin inheritance, rather than for de novo assembly. Importantly, we find that Fft3 bound to heterochromatic loci suppresses turnover of parental histones and is critical for the epigenetic transmission of heterochromatin in cycling cells. Surprisingly, Fft3 also localizes to several euchromatic loci where it is required for proper replication progression. Fft3 promotes nucleosome stability at these loci to prevent R-loop formation that can impede replication machinery. Strikingly, overexpression of the Clr4/Suv39h methyltransferase, which is also required for efficient replication through these loci, suppresses phenotypes associated with the loss of Fft3. Thus, we find that Fft3 promotes nucleosome stability to facilitate heterochromatin inheritance and also acts in parallel to Clr4 ensure proper replication of euchromatic regions. cdc25-22 cells carrying thymidine kinase and human nucleoside transporter expression modules were arrested at the G2/M boundary. After release into the cell cycle in minimal medium supplemented with hydroxyurea and 5’-bromo-2’-deoxyuridine (BrdU) cells were collected at time corresponding to maximal septation index and fixed by treatment with sodium azide. BrdU labeled DNA was recovered by immunoprecipitation, amplified by random-primed PCR and after conjugation with Cy5 (IP) or Cy3 (input DNA) analyzed on Agilent 60mer array.