LECTURE 6-Replication origins and ends regulation

LECTURE 6-Replication origins and ends regulation -...

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Accessory factors summary 1. DNA polymerase can’t replicate a genome. Solution ATP? No single stranded template Helicase   + The ss template is unstable SSB (RPA (euks))   - No primer Primase  (+) No 3’-->5’ polymerase Replication fork Too slow and distributive SSB and sliding clamp    -   Sliding clamp can’t get on Clamp loader ( γ /RFC)      + Lagging strand contains RNA Pol I 5’-->3’ exo, RNAseH   - Lagging strand is nicked DNA ligase    + Helicase introduces + supercoils  Topoisomerase II   + and products tangled 2. DNA replication is fast and processive
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DNA polymerase holoenzyme QuickTimeª and a DV - PAL decompressor are needed to see this picture.
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Maturation of Okazaki fragments
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Topoisomerases control chromosome topology Catenanes/knots Relaxed/disentangled Major therapeutic target - chemotherapeutics/antibacterials Type II topos transport one DNA through another       Topos
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Starting and stopping summary 1. DNA replication is controlled at the initiation step. 2. DNA replication starts at specific sites in E. coli and yeast. 3. In E. coli, DnaA recognizes OriC and promotes loading of the  DnaB helicase by DnaC (helicase loader) 4. DnaA and DnaC reactions are coupled to ATP hydrolysis. 5. Bacterial chromosomes are circular, and termination occurs  opposite OriC. 1. In E. coli, the helicase inhibitor protein, tus, binds 7 ter DNA  sites to trap the replisome at the end. 2. Eukaryotic chromosomes are linear, and the chromosome ends  cannot be replicated by the replisome.
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