Mutagenicity and repair of deaminated DNA lesions in prokaryotic and mammalian systems

The inheritance of traits from one generation to another is dependent on the integrity and stability of an organism's genetic material. In order to keep the integrity of its genome intact, cells must be able to counteract any type of exogenous measures that promote the modification of its DNA in any way. DNA damage occurs frequently even under normative conditions, and may come in many forms that may be summarized into one of three types: strand breakage, base modification and cross-linkage. However, for each of the many ways that DNA might be modified or damaged, the cell possesses a system by which either that damage might be reversed, removed, repaired or (if too extensive) controlled by programmed cell death. The majority of DNA repair occurs by one of several major pathways; the recombinational repair pathway, mismatch repair pathway, nucleotide excision repair (NER) pathway, base excision repair (BER) pathway or the endonuclease V repair pathway. The different elements that make up these pathways have all proven to be important to the health and survival of all organisms, and the disruption of such are manifested in human diseases that typically result in development of cancer, loss of cognitive abilities and premature death.; One of the more recently discovered DNA lesions is oxanosine. This lesion is a derivative of guanine that occurs due to a deamination of the N 1 amino group and its replacement with oxygen. In vitro studies have shown that upon treatment of deoxyguanine triphosphates with NaNO2 in acidic conditions, deoxyoxanosine triphosphate is produced as 20% of the deamination product (with deoxyxanthosine triphosphate as the remainder of product). In light of this observation, the mutagenicity of oxanine, as well as oxanine DNA glycosylase activities in mammalian systems have been studied. It has been found that using human polymerase beta, oxanine tends to be mutagenic if already found within the DNA template, but is not incorporated across from bases other than cytosine when in the nucleotide form. Oxanine DNA glycosylase (ODG) activity was detected in several mammalian cell extracts, and upon testing known mammalian DNA repair enzymes we have found human alkyladenine glycosylase (AAG) shows ODG activity. This study extends the deaminated base glycosylase activities of AAG to oxanine. Thus, AAG is a mammalian enzyme that can act on all three deaminated purine bases; hypoxanthine, xanthine and oxanine.; In addition to AAG, we have found that prokaryotes also posses systems by which oxanine lesions might be repaired. (Abstract shortened by UMI.)...