Repair replication in ultraviolet-irradiated HeLa-S3 cells was examined to determine the size distribution of the repair patches in the parental DNA. DNA containing patches of repair replication labeled with [3H]BrdUrd was isolated by CsCl isopycnic sedimentation. The repaired DNA was rebanded in alkaline CsCl after sonication (to reduce molecular weight to 0.2 · 106) or without sonication. The peak of repair label coincided with that of the parental density DNA in the larger fragments, and even in the very small fragments the two peaks nearly coincided. No large repair patches were evident, in contrast to the result in Escherichia coli in which most of the repair label appears in extremely large patches. From the shift observed in the smallest fragments (about 5 % of the distance between fully light parental DNA and BrdUrd-containing heavy DNA) the average size of repair patches in HeLa DNA was calculated to be about 30 nucleotides.
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