The specific heterodikaryon complementation results allowed us to allocate a 37-year-old female patient with xeroderma pigmentosum (XP31KO) to complementation group G of rare incidence. A mild form of XP31KO as the third group G patient manifested normal skin reaction to phototest, no physical or neuromental abnormalities, and a basal cell epithelioma, in contrast to the reference group G XP2BI. XP31KO cells showed 25% unscheduled DNA synthesis (UDS) after 10 J/m2 UV compared to less than 5% UDS in XP2BI cells and less hypersensitive responses to UV radiation and 4-nitroquinoline-1-oxide killings than did XP2BI cells. Such a repair phenotype of XP31KO presents an intragroup-G heterogeneity.
The specific heterodikaryon complementation method enabled us to assign three patients with mild xeroderma pigmentosum ( X P ) symptoms (XP25K0, XP27K0, XP28KO) to complementation group F. UV-induced unscheduled DNA synthesis (UDS) remained unnormalized in the heterodikaryons between either of the above three XP strains and the reference group F XP3YO. All these particular XP strains as well as XP3YO exhibited an equally low level of 10-15% UDS by a 3 h [3H]-thymidine labeling following 10 Jim2 254 nm UV, while they attained 60% UDS of normal at an extended time of 25 h. The present group Fstrains were 3 and I .S times as sensitive to the lethal effect of UV as normal and XP group E cclls. respectively, based on the mean lethal dose (Do) comparison. Normal cells had the biphasic time-UDS kinetics of early rapid and late slow repair. Characteristically, however, all of the present group F strains were defective in only early rapid repair, but normally proficient in slow repair.
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