Date of Award

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Biomedical Sciences

Track

Cell Biology and Biochemistry

Research Advisor

Janet F. Partridge, Ph.D.

Committee

Mark Bix, Ph.D. Paul K. Brindle, Ph.D. Linda M. Hendershot, Ph.D. Ronald N. Laribee, Ph.D.

Abstract

Eukaryotic DNA is packaged into the nucleus in complex with proteins that regulate access and utilization of the genetic material. These DNA and protein complexes form a dynamic structure known as chromatin. Nucleosomes are the repeating unit of chromatin, and consist of DNA wrapped around an octamer of histone proteins. Nucleosomes can then be modified and spatially arranged to facilitate processes such as transcription, DNA replication, and repair. A special transcriptionally repressive chromatin structure assembles onto gene-poor, repetitive regions of the genome known as constitutive heterochromatin. Mit1 is the putative chromatin remodeling subunit of the fission yeast Snf2/HDAC repressor complex (SHREC) and is known to repress transcription at regions of heterochromatin. However, how Mit1 modifies chromatin to silence transcription is largely unknown. Here we report that Mit1 mobilizes histone octamers in vitro Document Type: Doctoral Dissertation Name: Kevin M. Creamer Email Address: kevinmcreamer@gmail.com Title: The Mi-2 Homolog Mit1 Actively Positions Nucleosomes within Heterochromatin to Suppress Transcription Degree: Doctor of Philosophy Program (Major): Biomedical Sciences Concentration (Track): Cell Biology and Biochemistry Research Advisor: Janet F. Partridge, Ph.D. Advisor's Email: jpartri1@uthsc.edu Committee Members: Mark Bix, Ph.D. Paul K. Brindle, Ph.D. Linda M. Hendershot, Ph.D. Ronald N. Laribee, Ph.D. Keywords: chromatin remodeling, fission yeast, heterochromatin, Mit1, SHREC Availability: Embargoed for 12 months Graduation Date: May 2014 and requires ATP hydrolysis and conserved chromatin tethering domains including a previously unrecognized chromodomain to remodel nucleosomes and silence transcription. Loss of Mit1 remodeling activity results in nucleosome depletion at specific DNA sequences that display low intrinsic affinity for the histone octamer, but its contribution to antagonizing RNA Polymerase II access and transcription is not restricted to these sites. Genetic epistasis analyses demonstrate that SHREC subunits and the transcription coupled Set2 histone methyltransferase, which is involved in suppression of cryptic transcription at actively transcribed regions, cooperate to silence heterochromatic transcripts. In addition, we demonstrate that Mit1’s remodeling activity contributes to SHREC function independently of Clr3’s histone deacetylase activity on Lys14 of histone H3. We propose that chromatin remodeling by Mit1 cooperates with the Clr3 and other chromatin modifiers to stabilize heterochromatin structure and to prevent access to the transcriptional machinery.

DOI

10.21007/etd.cghs.2014.0059

Comments

One year embargo expired May 2015

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