Talk:CH391L/S12/MAGE lycopene production, CAGE "Amberless" E. coli

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*'''[[User:Jeffrey E. Barrick|Jeffrey E. Barrick]] 13:13, 14 April 2012 (EDT)''':There's an NAR paper about using modified bases in the oligos to avoid having to knock out MMR repair to get high efficiency incorporation. Can you summarize? <cite>Wang2011</cite>.
*'''[[User:Jeffrey E. Barrick|Jeffrey E. Barrick]] 13:13, 14 April 2012 (EDT)''':There's an NAR paper about using modified bases in the oligos to avoid having to knock out MMR repair to get high efficiency incorporation. Can you summarize? <cite>Wang2011</cite>.
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To avoid the MMR of ''L. reuteri'' the authors designed oligos with mismatch pairs to target the ''rpoB'' gene, which they had predicted the amino acid change would result in the rifampicin-resistant phenotype. Mutations such as C*C mismatch, which had been shown to be not efficiently recognized by ''E. Coli'' MMR were created in the oligos. MMR avoidance efficiency was determined by comparing rate of recombination of MMR deficient strains (mutS1- and mutL-). The oligo completely avoids MMR if it has a similar number of recombinations in wild type as it does in MMR deficient strains. The only oligo to completely avoid MMR was that with five consecutive mismatch mutations. <cite>Wang2011</cite> [[Image:L.reuteri.gif|thumb|200px|<cite>Wang2011</cite>]]
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To avoid the MMR of ''L. reuteri'' the authors designed oligos with mismatch pairs to target the ''rpoB'' gene, which they had predicted the amino acid change would result in the rifampicin-resistant phenotype. Mutations such as C*C mismatch, which had been shown to be not efficiently recognized by ''E. Coli'' MMR were created in the oligos. MMR avoidance efficiency was determined by comparing rate of recombination of MMR deficient strains (mutS1- and mutL-) with the wild-type strains. The oligo completely avoids MMR if it has a similar number of recombinations in wild type as it does in MMR deficient strains. The only oligo to completely avoid MMR was that with five consecutive mismatch mutations.<cite>Wang2011</cite> [[Image:L.reuteri.gif|thumb|200px|<cite>Wang2011</cite>]]
*'''[[User:Jeffrey E. Barrick|Jeffrey E. Barrick]] 13:22, 14 April 2012 (EDT)''': The MAGE papers cite beta as being the important activity, but also that the mechanism is not entirely understood. All of the strains used seem to have all three of the Lambda Red proteins (alpha, beta, gamma) integrated into their chromosomes in a way that they are induced at the same time? Here are some relevant strain construction details.
*'''[[User:Jeffrey E. Barrick|Jeffrey E. Barrick]] 13:22, 14 April 2012 (EDT)''': The MAGE papers cite beta as being the important activity, but also that the mechanism is not entirely understood. All of the strains used seem to have all three of the Lambda Red proteins (alpha, beta, gamma) integrated into their chromosomes in a way that they are induced at the same time? Here are some relevant strain construction details.
<blockquote>In brief, a defective Phage λ-Red construct was introduced by P1 transduction into E. coli MG1655 at the bioA location to produce EcNR1 (ΔbioA::λ-Red-bla). The relevant λ genes Redα, Redβ and Redγ are under regulation of the pL promoter and the temperature sensitive cI857 repressor. EcNR2 was made by using λ-Red homologous recombination to replace mutS with a chloramphenicol acetyltransferase (cat) cassette in EcNR1, thereby generating the ΔmutS::cat genotype. EcZS2 was made by introducing a kanamycin resistance (kan) cassette to replace the recA gene in EcNR1, generating a ΔrecA::kan genotype."<cite>Wang2011</cite></blockquote>
<blockquote>In brief, a defective Phage λ-Red construct was introduced by P1 transduction into E. coli MG1655 at the bioA location to produce EcNR1 (ΔbioA::λ-Red-bla). The relevant λ genes Redα, Redβ and Redγ are under regulation of the pL promoter and the temperature sensitive cI857 repressor. EcNR2 was made by using λ-Red homologous recombination to replace mutS with a chloramphenicol acetyltransferase (cat) cassette in EcNR1, thereby generating the ΔmutS::cat genotype. EcZS2 was made by introducing a kanamycin resistance (kan) cassette to replace the recA gene in EcNR1, generating a ΔrecA::kan genotype."<cite>Wang2011</cite></blockquote>

Revision as of 11:51, 16 April 2012

  • Jeffrey E. Barrick 13:13, 14 April 2012 (EDT):There's an NAR paper about using modified bases in the oligos to avoid having to knock out MMR repair to get high efficiency incorporation. Can you summarize? [1].
To avoid the MMR of L. reuteri the authors designed oligos with mismatch pairs to target the rpoB gene, which they had predicted the amino acid change would result in the rifampicin-resistant phenotype. Mutations such as C*C mismatch, which had been shown to be not efficiently recognized by E. Coli MMR were created in the oligos. MMR avoidance efficiency was determined by comparing rate of recombination of MMR deficient strains (mutS1- and mutL-) with the wild-type strains. The oligo completely avoids MMR if it has a similar number of recombinations in wild type as it does in MMR deficient strains. The only oligo to completely avoid MMR was that with five consecutive mismatch mutations.[1]
[1]
[1]
  • Jeffrey E. Barrick 13:22, 14 April 2012 (EDT): The MAGE papers cite beta as being the important activity, but also that the mechanism is not entirely understood. All of the strains used seem to have all three of the Lambda Red proteins (alpha, beta, gamma) integrated into their chromosomes in a way that they are induced at the same time? Here are some relevant strain construction details.
In brief, a defective Phage λ-Red construct was introduced by P1 transduction into E. coli MG1655 at the bioA location to produce EcNR1 (ΔbioA::λ-Red-bla). The relevant λ genes Redα, Redβ and Redγ are under regulation of the pL promoter and the temperature sensitive cI857 repressor. EcNR2 was made by using λ-Red homologous recombination to replace mutS with a chloramphenicol acetyltransferase (cat) cassette in EcNR1, thereby generating the ΔmutS::cat genotype. EcZS2 was made by introducing a kanamycin resistance (kan) cassette to replace the recA gene in EcNR1, generating a ΔrecA::kan genotype."[1]
  • Jeffrey E. Barrick 13:22, 14 April 2012 (EDT):What's the relationship of MAGE to "recombineering"?
    • James L. Bachman 11:04, 16 April 2012 (EDT):It seems that recombineering can be defined as "Engineering recombinant DNA molecules by in vivo homologous recombination".[1] The technique is based on the λ-Red system for either dsDNA or ssDNA incorporation. Since MAGE is an automated system that uses the λ-Red ssDNA incorporation as a means to generate recombination across the whole genome, it should be considered automated recombineering.
  • Jeffrey E. Barrick 13:24, 14 April 2012 (EDT):"Okazaki" is capitalized (it's someone's name). Please italicize E. coli.
  • Jeffrey E. Barrick 13:26, 14 April 2012 (EDT):Please summarize some of our discussion during class about how many cells die at each electroporation cycle, how much regrowth occurs between cycles, and the fact that apparently some portion of the population becomes "resistant" to MAGE.
    • James L. Bachman 10:29, 16 April 2012 (EDT):Through automating the MAGE process, the Church group was able to get MAGE cycles down to 2-2.5hr. At the electroporation step a high voltage of 18kV/cm was used, killing 95% of the cells in that cycle, which is then recovered to mid-log phase at a concentration of 7x10^8 cells/ml in liquid media for the next cycle.
  • Jeffrey E. Barrick 13:29, 14 April 2012 (EDT):Link to unnatural amino acid incorporation and genome synthesis topics?
    • James L. Bachman 10:29, 16 April 2012 (EDT):Added both, to note, whole-genome synthesis was actually talked about in the conclusion to the church MAGE paper.

References

  1. Wang HH, Xu G, Vonner AJ, and Church G. . pmid:21609953. PubMed HubMed [Wang2011]
    Modified bases enable high-efficiency oligonucleotide-mediated allelic replacement via mismatch repair evasion.

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