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Publication Date


First Advisor

Elizabeth R. Jamieson

Document Type

Honors Project

Degree Name

Bachelor of Arts




Nucleosomal, Base excision repair, Spiroiminodihydantoin, DNA lesion, Formamidopyrimidine DNA glycosylase


The integrity of the genome is continually threatened by oxidative damage to DNA which can cause carcinogenesis, aging, and neurological disorders.¹ Oxidative DNA damage is mediated by reactive oxygen species (ROS), leading to a wide variety of types of DNA damage, including DNA strand breaks, protein-DNA cross-links, abasic sites, and base lesions, which is potentially detrimental to cells.²⁻⁶

Among the four DNA bases, guanine is the most easily oxidized due to its low reduction potential.⁷ While more than 50 different oxidative DNA lesions have been discovered, one of the most extensively studied is 7,8-dihydro-8-oxo-2’-deoxyguanine (8oxoG).⁸

The spiroiminodihydantoin (Sp) lesion, the focus of this project, is a hyper- oxidation product of guanine and has gained attention due to its unusual structures and high mutagenic potential. Unlike planar 8oxoG, Sp lesions are highly mutagenic, chiral, propeller shaped lesions, and both diastereomers can destabilize the double stranded DNA structure.⁹

Given the high mutagenic potential of the Sp lesion, it is imperative that this oxidized base be repaired in order to ensure the integrity of the genome. Studies have been well- established on the ability of the Base Excision Repair (BER) system to act on both diastereomers of Sp ¹⁰ This lesion is known to be repaired by E. coli DNA glycosylases including Formamidopyrimidine DNA Glycosylase (Fpg).¹¹⁻¹² DNA glycosylases remove the Sp lesion from various substrates through the BER mechanism including single- stranded and duplex DNA. Therefore, examining the repair of the Sp lesion in more complex structures may be relevant biologically as such structures may play regulatory roles in gene transcription and telomeric DNA elongation.¹³

The specific focus of this research project is to examine 8oxoG lesion repair by the DNA glycosylase, Fpg, in nucleosomes through the BER mechanism. The ultimate goal of this project is to demonstrate that the E. coli DNA glycosylases which have been shown to repair the 8oxoG lesion can repair the Sp lesion. We will also investigate the rate of excision of Sp from nucleosomal DNA.


©2020 Linghe Zhang. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.




100 pages : illustrations (some color) Includes bibliographical references (pages 92-100)