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320-21posted1 - Lecture 21 Gene expr essi on i n eukar...

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Chromosome features Centromeres and telomeres Transposons: mobile chromosome elements. Chromatin & gene expression Nucleosomes & DNA packaging Chromatin modification & gene expression • Position effects & X inactivation Lecture 21 Gene expression in eukaryotes
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Eukaryotic chromosomes & gene regulation Chromosome features Ch 13.1-13.3 Centromeres and telomeres Transposons: mobile chromosome elements. Chromatin & gene expression Ch 13.4 Nucleosomes & DNA packaging Nuclease hypersensitivity • Position effects & X inactivation Regulating gene transcription Ch 18.1-18.2 Enhancers & DNA-binding proteins Signal transduction Epigenetics • DNA methylation; genomic imprinting Regulation after transcription Ch 18.3-18.4 Gene regulation by splicing RNA interference Ridley ch 15 “SEX” Lectures 21 - 22 Ch 14.1
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Chromosome anatomy Telomeres enable end replication not subject to repair only one per chromosome! Centromere Chromosome functions: replication and segregation Origins of replication many per chromosome spindle microtubules kinetochore microtubule attachment
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fluorescent antibody to CENP-E protein Specific proteins assemble at centromeres and kinetochores
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Telomere replication (lecture 9) 5’ 3’ 5’ 3’ 3’ 5’ 5’ 3’ ??
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fluorescent probe for TTAGGG Telomerase: inactive in adult somatic cells - telomeres get shorter reactivated in many tumor cells - cells are “immortalized”
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Transposons: mobile elements in genomes Dispersed repeats… …originate as transposable elements = mobile genetic elements = transposons : = DNA segments that can move from place to place in the genome. DNA transposons Depend on recombination activity of a DNA transposase Retrotransposons . Transpose via an RNA intermediate ; require reverse transcriptase First discovered in corn ( in 1940s, at CSH, by Barbara McClintock) as “controlling elements” that could move from one locus to another. Ch 14 pp 508-514
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DNA transposons Transposase gene Autonomous element: self-sufficient Non-autonomous derivative: - transposase gene mutated or lost; moves only if enzyme supplied by another element. Inverted repeats
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Examples of DNA transposons - Insertion sequences (IS’s) in bacteria - mediate F plasmid insertion into & excision from chromosomal sites. - Ac (autonomous) & Ds (nonautonomous) elements in corn - if insertion affects kernel color, color restored on excision in somatic cells: mosaic pattern produced. - P elements in Drosophila - invaded D. melanogaster worldwide in <50 years - useful for transgenics, and as mutagen. YFG white +
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RNA transposons 1 2 LTR LTR Proof of RNA intermediate: Cloned yeast Ty1 element, added intron: Intron spliced out in new insertions! Transformed into in yeast, looked for new transposition events: Fig. 14.26
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Examples of RNA transposons Retroviruses: infectious retrotransposons LTR LTR gag pol env encode viral coat & envelope proteins Most dispersed repeats in the human genome are “fossil” type 1 retrotransposons LINEs AAAAAAAA TTTTTTTT e.g. LINE-1, 1.4kb, 100,000x SINEs AAAAA TTTTT e.g. “Alu” element: 180-280 bp, 300,000x Genetic parasites - “selfish DNA”. Ridley Ch 8 - “Self-interest All SINES + LINES : c. 35% of genome!
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