Experimentation was performed primarily to determine whether progression of the DNA replication fork along segments of S phase Xenopus chromosomes, which contain UV-induced pre-aberrational lesions, plays a significant role in conversion of these lesions into chromatid deletions. Specifically, a Xenopus chromosome that was both easy to identify and that possessed a single DNA replication fork in one arm was found and used to conduct the experimentation. This chromosome was exposed to UV in early S phase and a Bromodeoxyuridine/Giemsa differential staining technique was applied in conjunction with conventional aberrational techniques to correlate progression of the DNA replication fork through segments of this arm with chromatid deletion production in these segments. The results point to "direct" evidence for the role of the DNA replication fork in converting some UV-induced pre-aberrational DNA damage into chromosomal deletions.

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