A biological dosimeter has been developed for use in aquatic environments. This method is based on the sensitivity of a DNA repair-deficient strain of Escherichia coli (CSR06) to ultraviolet (UV) radiation. The dosimeter permits evaluation of the penetration of biologically active UV radiation within a water column, reflecting the potential effect of exposure over selected time intervals. With the use of various filters, the biological dosimeter can discriminate between the effects of UV-B (280-320 nm) and UV-A (320-400 nm) or other selected portions of the solar UV spectrum. During springtime ozone depletion over the Antarctic in 1988, a general relationship was observed between stratospheric ozone concentration and the contribution of incident solar UV-B radiation to lethality of dosimeter cells. The use of dosimeters within the water column indicated that significant amounts of UV-B can be transmitted to a depth of 10 m and biological effects of UV could be detected to 20 and 30 m. Biological dosimeters may provide a means of standardizing in-water UV measurements across all types ofaquatic habitats and at any geographical location.The intensity and spectral distribution of radiation at the earth's surface are dependent on factors such as solar output, weather, and spectral absorbance of atmospheric gases and particles (both naturally occurring AcknowledgmentsWe thank A. Sancar and G. B. Sancar for the gift of the CSR06 cell line, H. Steier and M. Harrington for help in design and construction of sampling frames, D.

A group A xeroderma pigmentosum revertant with normal sensitivity was created by chemical mutagenesis. It repaired (6-4) photoproducts normally but not pyrimidine dimers and had near normal levels of repair replication, sister chromatid exchange, and mutagenesis from UV light. The rate of UV-induced mutation in a shuttle vector, however, was as high as the rate in the parental xeroderma pigmentosum cell line.Xeroderma pigmentosum (XP) is a human recessive disorder that in the homozygote exhibits a large increase in skin cancer induced by sunlight (5). The sensitivity of XP cells in culture to UV light (254 nm) is 5-to 10-fold greater than nQrmal (1,15), and the cells fail to repair a wide range of radiation-and chemically induced DNA damage (5, 10, 27), including (5-5,6-6)cyclobutane pyrimidine dimers and (6-4) pyrimidine-pyrimidone photoproducts, measured by radioimmunoassay (4, 19-21) and enzymatic methods (7,13,14,44). The relative proportions of cyclobutane dimers to other photoproducts determined from their photoreactivation suggest that (6-4) photoproducts may account for as much as 30% of the total lesions (24), and they are highly mutagenic (2). One of the problems encountered in attempts to clone the XP gene results from the reversion of the XP phenotype to UV resistance (16,28,29); therefore, we decided to fully characterize revertants themselves.XP12RO (a simian virus 40-transformed group A cell line), GM637 (a simian virus 40-transformed normal cell line), and normal fibroblasts (HS27 and AG) were grown in Eagle minimal essential medium with fetal calf serum, penicillin, and streptomycin. The XP12RO cell line was cloned by choosing a single colony from among those that grew from a culture of 100 to 200 cells. Large cultures (107 to 108 cells) of XP12RO were exposed to ethyl methanesulfonate at a concentration of 1, 3, or 6 mM in culture medium for 16 h, after which the medium was replaced and the cultures were grown for 1 week. The cultures were subsequently transferred on regular occasions (approximately twice per week), based on the cell density. They were irradiated in phosphate-buffered saline with 1 to 3 J of UV light per m2 (254 nm; 1.3 J/m2 per s) at each transfer. After an accumulated dose of approximately 60 J/m2, the cultures were given a dose of 6.5 J/m2 and allowed to grow for 3 weeks to produce colonies. One colony was chosen for each ethyl methanesulfonate dose and grown into a large culture for subsequent analysis. Cell survival after UV irradiation was determined from the number of macroscopic colonies (>50 cells) formed in 21 days (J. E. Cleaver and G. H. Thomas, J. Invest. Dermatol., in press). Each of the cell lines derived from XP12RO proved to be resistant to UV light (Fig. 1A), and, accordingly, they were defined as revertants (designated XP129, XP322, and * Corresponding author. XP644). When similar-size cultures were not exposed to ethyl methanesulfonate, no surviving colonies were recovered. Revertants showed intermediate sensitivities to 4-nitroquinoline-1-oxide (4NQO) (Fig....

Rejoining of DNA double-strand breaks (DSB) plays a central role in the various processes leading to DNA rearrangements. We have analyzed DNA alterations induced by restriction enzymes that produce DSB with specific types of ends. Restriction enzymes were electroporated into a human lymphoblastoid cell line that stably maintains pHAZE, an EBV-based vector containing the lacZ gene. After allowing time for DSB repair, pHAZE DNA was rescued and screened in Escherichia coli. Mapping and sequence analysis of mutant copies of pHAZE indicated that restriction enzymes induced all classes of alterations except base substitutions (base deletions and insertions, large-scale deletions, inversions, and insertions). The spectra of alterations were distinctive for each enzyme and appear to be the consequence of specific end-modification processes.

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