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Bi190 2005 Sternberg Analyzing and Building Chromosomes

Bi190 2005 Sternberg Analyzing and Building Chromosomes. Three types of DNA sequence required for eukaryotic chromosomes. Replication origin (many per chromosome) functions in interphase to duplicate DNA. Centromere (one per chromosome) functions in mitosis for chromosome segregation.

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Bi190 2005 Sternberg Analyzing and Building Chromosomes

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  1. Bi190 2005 Sternberg Analyzing and Building Chromosomes

  2. Three types of DNA sequence required for eukaryotic chromosomes Replication origin (many per chromosome) functions in interphase to duplicate DNA. Centromere (one per chromosome) functions in mitosis for chromosome segregation. Telomeres (two per chromosome) cap the chromosome ends.

  3. The kinetochore forms in mitosis at the centromere

  4. The primary constriction occurs at the centromere of a mitotic chromosome

  5. In Situ Hybridization of Human Chromosomes With a Probe Against the Telomere Repeat

  6. Selection of Centromere DNA in Budding Yeastyeast functional assays for (a) ARS (b) centromere (c) telomere

  7. Selection of Centromere DNA in Budding Yeastyeast functional assays for (a) ARS (b) centromere (c) telomere

  8. Szostak & Blackburn (1982) Tetrahymena rDNA: 21 kb small linear molecule Tel + HIS3+ Bam H1 Bam H1 Bgl II Tel Tel CCCCAA Bam H1 Bgl II Bam H1 Bgl II LEU2+ ars1 Col E1 ori AmpR GGGGTT Of 15 Leu+ transformants, 14 were mitotically unstable; 1 integrant. ~20 copies per cell, and LINEAR! by R-Mapping

  9. Clone a yeast telomere: Pvu I T.TEL LEU2 yeast DNA yeast DNA, cut with Pvu I into ~2000 pieces 32 should be telomeres (1/65) Of 60 colonies, 56 had plasmid (mitotically unstable) Pick 3 that had a small single Pvu I fragment--- A yeast TEL 5´ ... C G A T^C G ... 3´ 3´ ... G C^T A G C ... 5´

  10. Murray & Szostak TEL YLp4 transform yeast TEL Plate 100 colonies/plate replica plate to -Leu count fraction Leu+ LEU2+ CEN3 ARS1 Col E1 ori AmpR plasmid %cells Segr. copies/cell with plasmid Freq. circle - 5 0.34 50 circle CEN 90 0.02 1 YLp4 CEN 61 0.11 15 YLp30 - 72 0.16 50 Pedigree analysis to determine the segregation frequency, the fraction of divisions at which only one daughter receives the plasmid TEL inhibits CEN function; yeast chr are 10-100 fold longer

  11. Telomere Repeats of Some Organisms NB – 3’ overhang is G-rich

  12. human artificial chromosomes [Harrington….Willard, 1997) linear, mitotically stable CEN TEL ORI transfect in alpha-satellite, TTAGGG (TEL), selectable marker and obtain a minichromosome. After 240 generations with no selection, 29-100% had the mini 99.5% segregation frequency.

  13. Tandem repeats of alpha satellite DNA constitute a primate centromere[Schueler, Higgins, Rudd, Gustashaw and Willard, Science (2001)] • Chromosome rearrangements define the CEN as (171bp)12 • Artificial chromosomes with 85 Kb alpha satellite DNA (red) bind the centromere protein CENP-E (green). Overlap of both is yellow.

  14. Centromere Sequences Differ Between Organisms Epigenetic model: something else besides DNA sequence may define a centromere

  15. Analysis of CEN Mutations by DNA Sequence Replacement in Budding Yeast(Rothstein) ds replacement DNA ds chromosomal DNA homology homology ds chromosomal DNA with replacement

  16. Double-strand break repair model invasion invasion

  17. Transposon-induced Gap repair a b a b a b a b a b a b a b a b

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