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Title: Repair of UV induced DNA damages in Escherichia coli
Author: Li, S.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1997
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A new method for the nucleotide level detection of cyclobutane pyrimidine dimers (CPDs) is presented. Using this method, I investigated the induction and repair of CPDs in the E. coli tRNA gene tyrT. The transcription stimulator Fis affects induction of CPDs in the gene control region. In stationary cells, slow, similar rates of repair occurred throughout the non-transcribed strand (NTS). Faster repair occurred in the NTS control region in log phase. Heterogeneous repair occurred along the transcribed strand (TS). In the control region repair was faster than in the NTS. When irradiation log phase cells were in rich medium, transcription-coupled repair (TCR) occurred in a small domain of the coding region within 31 nucleotides from the transcription start site, but was absent in the large domain composed of the rest of the TS coding region. In similarly treated stationary phase cells, TCR occurred throughout the TS coding region. Depletion of Fis reinstates TCR in the large domain to a lesser extent. TCR is reinstated by disruption of Fis binding to the upstream activating sequence or by incubating irradiated cells in minimal salt medium without the required amino acid. The results suggest Fis indirectly suppresses TCR in the TS large domain by stimulating transcription. E. coli strains lacking the histone-like protein HU are UV sensitive in the backgrounds of rec+ sbc+, recBC sbcA and recBC sbcBC. Although they dramatically enhance the UV sensitivity of uvrA, umuDC, recG, recF and recD strains, hupAB mutations only slightly enhance the UV sensitivity of ruvA, strains, and do not enhance the UV sensitivity of resolvase-deficient recG ruvA strains. My results suggest HU plays a role in recombinational DNA repair that is not specifically limited to double strand break repair or daughter strand gap repair; the function of HU is not in the substrate processing step or in the RecFOR-directed synapsis action during recombinational repair.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available