Precise’Manipulaon’of’ Chromosomes’in’Vivo’Enables ... · Precise’Manipulaon’of’...
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Precise Manipula.on of Chromosomes in Vivo Enables
Genome-‐Wide Codon Replacement
Isaacs, Farren J. et al. Science, Vol 333, 2011
Presented by: PJ Velez
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Useful Defini.ons
• Conjuga.ve Assembly genome engineering (CAGE) Method -‐ Large Scale Engineering
• Mul.plex Automated Genome Engineering (MAGE) Method – Small Scale Engineering
• λ Red Protein-‐ Proteins that promote recombina.on and are mutagenic.
• RF1/RF2 – Release factors in E. Coli that recognize stop codons
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Goals and Mo.va.on
• Long Term Goal: Successfully modify gene.c code
• Long Term Impact: – Novel Biological System Proper.es – Easier incorpora.on of unnatural Amino Acids
• Short Term Approach: – Replace all TAG stop codons with TAA in viable E. Coli • RF1 dele.on mutant s.ll viable
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Overall Strategy
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MAGE
• Genome split into 32 regions of <10 genes with TAA codon
• 18 MAGE Cycles • Assays to iden.fy greatest number of codon conversion and measure frequencies
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MAGE
• Some Cells more suscep.ble to muta.ons
• Top clone found for each region
• Also looked at poten.al unintended muta.ons – BLAST – Sanger Sequencing
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CAGE
• 32 clones put into pairs – Donor Strand
• oriT-‐kan and posi.ve selectable marker
– Recipient Strand • Posi.ve-‐Nega.ve selectable marker and different posi.ve marker
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Final Experiments
• Performed genome sequencing on two dysfunc.onal strains and a control aber MAGE/CAGE – 1 error per genome per 9 replica.ons
• Hypergeometric distribu.on – Determine enrichment level across three strains
• Problem: No figures or data shown in paper – Buried in 90 pages of supplement
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Conclusions and Future Direc.ons
• Successfully replaced all TAG occurrences with TAA codons
• Improve future genome engineering efforts – Dynamic method to introduce change in cell
• Help refine exis.ng genome annota.on
• Already been cited four .mes – Came out last July
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Supplementary Slides for Discussion
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Issues with Final Figure
• Overall layout not really specified – Media?
– Order of Rows? – Yellow Arrows?
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Other points for Discussion
• Successfully show what they set to? • Final Experiments worthy of being published?
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MAGE
• Sanger Sequencing verified presence of conversion and secondary muta.ons
• Look at 300 bp surrounding replaced site