DNA-to-protein Cross-linking in Synchronized HeLa Cells Exposed to Ultra-violet Light

Abstract

The U.V.-induced DNA-to-protein cross-linking in synchronously growing HeLa cells exhibits age-dependent variations. The maximum yield of cross-linking is observed during S-phase and exposure of mid-S cells to 250 ergs/mm2 renders about 22 per cent of DNA unextractable owing to cross-linking with proteins. Cells irradiated in G1 or G2 exhibit much smaller amount of cross-linking. The unextracted DNA was recovered from the protein fraction, and the addition of 0-5 per cent trypsin solution rendered all the DNA extractable. Fluctuations in the age-response pattern for the yield of DNA-protein cross-links varies throughout the cell-cycle in the same way as the efficiency for cell-killing, i.e. cells are resistant in G1, sensitive as they move into and through the S phase, and resistant again in G2. Dose-response curves determined at different times in the cycle reveal that up to about 500 ergs/mm2 the amount of DNA recovered from S cells decreased for about 8 per cent for every 100 ergs/mm2 of U.V. light. The amount of recovered DNA remained unchanged for cells exposed to 500 ergs/mm2 in the middle of S, for as long as 8 hours after exposure, i.e. for as long as the experiments were carried out no recovery from this damage was observed.

Cross-Linking of Proteins to Nucleic Acids by Ultraviolet Light

“…The amount of unextractable DNA maintained a constant value in cells incubated for periods of time up to ten hours after the termination of irradiation. Han et al (1975) studied the UV induction of DNA-protein cross-links in synchronized HeLa cells as a function of cell cycle phase. They found that the synchronized cells were most susceptible to cross-linking in S phase; cells irradiated in G1 or G2 phase displayed significantly decreased susceptibilities.…”

Non‐dimer Dna Damage in Chinese Hamster V‐79 Cells Exposed to Ultraviolet‐b Light

“…In general, it has been known that UV light produces various kinds of DNA lesions besides pyrimidine dimers, i.e. single strand breaks (Elikind and Han, 1978;Miguel and Tyrrell, 1983;Peak et al, 1987;Rosenstein and Ducore, 1983), DNA-protein crosslinks (Chiu et al, 1984;Fornace and Kohn, 1976;Han et al, 1975;Lai et al, 1987;Peak et al, 1985a,b), DNA double strand breaks (Bradley and Taylor, 1981) and thymine glycol (Hariharan and Cerutti, 1977). The present paper compares a number of measurements, including the repair of non-*To whom correspondence should be addressed.…”

Absence of Repair of Sublethal U.V. Light Damage in Chlamydomonas

“…exposure during which lesions other than the pyrimidine dimer are accumulated . This second type of lesion could, for example, be a cross-link between DNA and protein of the type described by Han, Korbelik and Ban (1975) .…”