Defense Date


Document Type


Degree Name

Doctor of Philosophy


Pharmacology & Toxicology

First Advisor

Lawrence F. Povirk


Previous studies suggested that teniposide is a strong clastogen, and that the DNA breakage effect of this drug is mediated by the nuclear enzyme topoisomerase II. Ripley et al found evidence for a correspondence between sites of acridine-induced frameshift mutations in bacteriophage T4 and sites of in Vitro DNA cleavage by T4 topoisomerase II. To identify the sequence specificity of teniposide-induced deletion and insertion mutations in mammalian cells, the CHO-D422 cell line, which is hemizygous at the aprt locus, was employed in this study. Sixty-eight teniposide-induced and 42 spontaneous aprt mutants were analyzed at the DNA sequence level. Compared with the spectrum of spontaneous mutations in which two thirds of the mutations are base substitutions, two thirds of teniposide-induced mutations are deletions and insertions of different sizes. Significant site correspondence between teniposide-induced deletion/insertion mutations and in vitro DNA double strand cleavages by purified mammalian topoisomerase II was also found in this study, which suggests that the majority of teniposide-induced deletions and insertions observed in this study were generated at the sites of topoisomerase II mediated DNA double strand breaks in the cells. However, considering the positions of the double cleavage sites in the mutation sequences, no consistent pattern was found which could suggest a unified mechanism of DNA double strand break repair. Three models are proposed to try to explain the possible events occurring in the cells following teniposide exposure which resulted in observed deletion and insertion mutations.


Scanned, with permission from the author, from the original print version, which resides in University Archives.


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