Of all exogenous agents that damage genomic DNA and hence threaten its integrity, the ultraviolet B (UVB) component of sunlight is highly relevant because of its abundance. UVB induces... Show moreOf all exogenous agents that damage genomic DNA and hence threaten its integrity, the ultraviolet B (UVB) component of sunlight is highly relevant because of its abundance. UVB induces predominantly cyclobutane pyrimidine dimers and 6-4 photoproducts. In humans, these photolesions are repaired by the nucleotide excision repair (NER) system. Additionally NER removes a range of bulky, helix-distorting lesions, including chemical adducts caused by the anticancer drug cisplatin and complex hydrocarbons found in burnt food and cigarette smoke. Patients suffering from xeroderma pigmentosum, an inherited disorder caused by mutations in genes encoding NER proteins, display hypersensitivity to sunlight and a dramatically increased incidence of skin cancers. The research in this thesis concerns NER in intact human cells. Findings include: 1) the NER complex assembles on a lesion in a sequential manner, as opposed to pre-existing as a holo-complex; 2) TFIIH is not involved in the UV-induced inhibition of transcription; 3) XPA is not complexed with RPA, contradicting previous reports; 4) UV-DDB stimulates the repair of low levels of 6-4 photoproducts; and 5) pol_, pol_ and ligase I are involved in the DNA resynthesis step of NER in vivo. Show less
