Summary
Thymidine incorporation by HEp-2 cells was reduced 10-fold by 2.5 mm hydroxyurea (HU). The DNA in lysates from untreated cells sedimented through alkaline sucrose gradients as an aggregate plus a smaller component which could be chased into the aggregate. Only small DNA (ca. 47 S) was synthesized in nuclei when cells were incubated with HU. HU inhibition was reversible up to 24 hr. Removal of inhibitor was followed by the conversion of small DNA into rapidly sedimenting material. After 24 hr incubation with HU, an increasing percentage of the small DNA failed to join the aggregate. At about this time, fragmentation of native DNA molecules was observed, and there was a decrease in viability as measured by colony formation. The accumulation of double-strand breaks in DNA from cells incubated in the presence of HU presumably represents irreparable lethal damage.
Footnotes
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↵1 Supported in part by NIH Grant 2 R01 GM 07816, National Science Foundation Grant GB 5814, the Atomic Energy Commission Grant AT(11-1) 2040.
- Received March 2, 1970.
- Accepted May 8, 1970.
- ©1970 American Association for Cancer Research.