The Mi-2 homolog, Mit1, actively positions nucleosomes within heterochromatic domains to suppress transcription

Nucleosome positioning is both active and passive and regulates access to the genome for replication, transcription and repair. Here we report that Mit1, a subunit of the fission yeast SHREC complex similar to Mi-2/NuRD, regulates transcription at regions of heterochromatin by positioning nucleosomes to preclude access to RNA Polymerase II. Purified Mit1 is a nucleosome remodeling factor capable of mobilizing histone octamers on short DNA fragments and requires ATP hydrolysis and chromatin tethering domains to remodel nucleosomes and silence transcription. We propose that SHREC is recruited to heterochromatin to mobilize nucleosomes onto unfavorable positions to prevent spurious transcription within heterochromatin. RNA samples were prepared from biological duplicates of WT and mit1∆::NatMX6 fission yeast to compare transcript levels using the Affymetrix GeneChip S.pombe Tiling 1.0FR microarray.