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

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. Overall design: 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.

核小体定位（nucleosome positioning）兼具主动与被动调控模式，可调控基因组在复制、转录与修复过程中的可及性。本研究发现，Mit1作为裂殖酵母SHREC复合物的亚基，其功能类似Mi-2/NuRD复合物，可通过定位核小体阻断RNA聚合酶II（RNA Polymerase II）的结合，从而调控异染色质区域的转录。纯化获得的Mit1是一种核小体重塑因子，能够在短DNA片段上移动组蛋白八聚体（histone octamers），其发挥核小体重塑与转录沉默功能需要ATP水解能力及染色质锚定结构域。本研究提出，SHREC复合物被招募至异染色质区域后，会将核小体移动至不利位置，以阻断异染色质区域内的异常转录。实验设计概述：本研究分别制备野生型（WT）与mit1Δ::NatMX6裂殖酵母的生物学重复RNA样本，通过Affymetrix GeneChip S.pombe Tiling 1.0FR微阵列比较两组样本的转录本水平。