Page 17 - Academic Press Encyclopedia of Physical Science and Technology 3rd Molecular Biology

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Encyclopedia of Physical Science and Technology EN002G-104 May 17, 2001 20:53

Chromatin Structure

and Modification

Fyodor D. Urnov
Alan P. Wolffe
Sangamo Biosciences

I. The 6-Billion Challenge
II. Chromatin: A Brief History of Scholarship
III. Chromatin Structure: The Histones
and the Nucleosome
IV. The Disruption and Modification of Chromatin
Structure as a Tool to Control the Genome
V. Chromatin and Transcription: A Synthesis

GLOSSARY core histones’ amino terminal tail. Commonly used in
transcriptional repression.
Chromatin A complex between genomic DNA and pro- Histone Small (ca. 110 amino acids), highly basic pro-
teins (mostly histones) that compacts the genome into tein that is rich in lysine and arginine. Assumes a dis-
the eukaryotic nucleus and enables its functionality. tinctive 3-helix “histone fold” tertiary structure with
DNA methylation The covalent modification of cytosine an extended amino terminal tail. Four “core” his-
to yield 5-methylcytosine. In vertebrates occurs ex- tones (H2A, H2B, H3, H4) form an octamer that
clusively within the context of a CpG dinucleotide. winds DNA onto itself to form the nucleosome core
Produced by DNA methyltransferase and interpreted particle.
by dedicated DNA-binding proteins that effect tran- Nuclear hormone receptor (NHR) A transcription fac-
scriptional repression in part via recruiting histone tor whose activity is regulated by a small molecule
deacetylase. (the ligand), such as a steroid (estrogen, cortisol, etc.)
HAT Histone acetyltransferase. Enzyme that catalyzes or an amino acid (thyroid hormone). Most NHRs are
the acetylation of the ε-NH 2 group in the side chain transcriptional activators in the presence of ligand;
of lysine residues in the core histones’ amino terminal some NHRs also act as transcriptional repressors in
tail. Commonly used in transcriptional activation. its absence.
HDAC Histone deacetylase. Enzyme that catalyzes the Locus (pl. loci) Geneticists’ term for “specific location
removal of the acetyl residue from ε-acetyllysine in the on the chromosome (in the genome).”

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