Alternative nucleosomal structure
Dalal, Yamini Laboratory of Receptor Biology and Gene Expression, Cancer Center for Research, National Cancer Institute, Bethesda, Maryland.
- Histone variants, epigenetics, and mitosis
- Altered centromeric nucleosomal organization
- Alternative nucleosomal structure and epigenetic inheritance
- Future outlook
- Links to Primary Literature
A fundamental innovation that distinguishes eukaryotes from bacteria is the way in which the genome is organized. In bacteria, DNA is a naked circular molecule. In eukaryotes ranging from yeast to humans, DNA is packaged into chromatin, which is composed of beadlike structures called nucleosomes. Each nucleosome contains two copies of the histone proteins, H2A, H2B, H3, and H4, and wraps 147 base pairs (bp) of DNA in a left-handed ramp, resulting in a conserved octameric structure (Fig. 1). In addition to packaging DNA, nucleosomes can impede access to regulatory regions and genes. This is referred to as epigenetic control because it provides a layer of information above the genetic code, which itself is embedded within the DNA sequence. The epigenetic status of the genome plays a crucial role in regulating gene expression, DNA repair, DNA accessibility, and DNA segregation. Consequently, it has enormous significance in the biology of normal and diseased cells.
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