Lidstrom:UV Mutagenesis

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Basics of UV mutagenesis

  • In C. elegans, UV mutagenesis is better than EMS mutagenesis for large deletions and rearrangements. (Anderson 1995)
    • Note, however, the effect of mutagens is different on different hosts so this may not be true for your bacterium.

Reasons AM1 has been mutated with EMS, not UV

  • The genome is GC rich.
    • Since UV makes TT dimers, you get less mutations and they are more frequently right before genes where the DNA tends to be AT rich.
  • It is pink, so it absorbs the UV radiation to some degree.
    • JM doesn't think this should matter much. It should just mean that you need a larger dose.

Resources

  • UV Radiation and Spontaneous Mutagenesis: summary by Kendric C. Smith, Emeritus Professor, Radiation Oncology (Radiation Biology), Stanford University School of Medicine
    • Discusses repair mechanisms a lot.
    • UV radiation produces a preponderance of alterations in the pyrimidines, and the large majority of these products involve the linking of two adjacent pyrimidines
    • "G:C -> A:T transitions predominate after UV irradiation.
      • In E. coli the (6-4)-photoproduct may be more important for mutagenesis, while the pyrimidine dimer may be more important in mammalian cells. In human cells, mutations occur at the C of a TC, CT, or CC pyrimidine dimer, but not at TT dimers, and also occur at the C of TC and CC (6-4)-adducts (reviewed by Brash, 1988)."
    • UV-radiation-induced mutations show 2-hit kinetics at high doses
      • i.e., they are produced as a function of the square of the dose
    • While UV irradiation does not produce DNA double-strand breaks directly, they can be formed as a consequence of the inefficient repair of overlapping excision gaps, and of overlapping daughter-strand gaps
    • The formation of DNA-protein cross-links has been shown to be of significance in the killing of E. coli
    • In general, UV irradiation produces mutations along a gene in a non-random manner, i.e., mutations are observed at certain base pairs more frequently than at others
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