Chromatin Lecture 1 2013.pdf

Cr length of dna in the core particle dimension of

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CR = Length of DNA in the core particle / dimension of core particle 146 bp X .34 nm/bp 6 nm = 8.3 OR 146 bp X .34 nm/bp 11 nm = 4.5 How much does a nucleosome change the “effective” length of DNA?
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A Higher Order Chromatin Fibre (?)
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Figures in following slides from Molecular Biology of the Gene, 5 th Ed, Watson et al ., Pearson Education, Inc., San Francisco
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1 mM TEACl, EDTA 5 mM TEACl, EDTA 40 mM NaCl, 5 mM TEACl 100 mM NaCl, 5 mM TEACl from Thoma et al (1979) J Cell Biol 83, 403-427
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Heterochromatin and Euchromatin cytological and cytogenetic definitions Heterochromatin
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Late-replicating heterochromatin can be distinguished in metaphase and interphase Carmo-Fonseca (2002) Cell 108, 513 FISH probe FISH probe
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Timing of replication correlates with nuclear location: expressed genes generally replicate early Swedlow and Lamond (2001) Genome Biology 2, 2.1-2.7 Block cells at G1/S with aphidico Release and pulse label with Brd Immunofluorescence labelling o halogenated DNA
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Chromatin : Structure package DNA AND A Regulatory Role open and closed states
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Two functions of histone modifications: (1) structure/stability of nucleosome, (2) binding of other regulators
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from Robertson and Wolffe (2000) Nat Rev Genetics 1, 11-19 A transcriptionally active region targeted for silencing is proposed to acquire DNA methylation first, which then recruits the methyl-CpG binding proteins and their associated co-repressors and histone deacetylases (HDACs). As DNA methyltransferase 1 (DNMT1) can interact directly with histone deacetylase, it is also possible that transcription is first silenced by deacetylation by other tethering factors, after which the methylation machinery and the methyl-CpG binding proteins are recruited to 'cement'the promoter in the silent state. In either case, the deacetylated nucleosomes adopt a more tightly packed structure that inhibits the access of transcription factors to their binding sites.
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* **
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Chromocentres: densely-packed heterochromatin, marked with H3K9Me3 and H4K20Me3 from Gunnar Schotta, Ludwig-Maximillians U FISH probe Chromocentres
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Confocal images of indirect immunofluorescence for H3K9me3 and H3K27me3 in growing and Ras-senescent IMR90 cells. Arrows indicate inactive X chromosomes. Chromatin reorganization with senescence Formation of Senescence Associated Heterochromatin Foci (SAHFs) Tamir Chandra, Dr. Masashi Narita
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