SISTER CHROMATID EXCHANGE IN XERODERMA PIGMENTOSUM CELLS THAT ARE DEFECTIVE IN DNA EXCISION REPAIR OR POST-REPLICATION REPAIR

Sheldon Wolff ¹, Judy Bodycote ², G. H. Thomas ², and James E. Cleaver ²

¹ Laboratory of Radiology and Department of Anatomy University of California, San Francisco, California 94143
² Laboratory of Radiology University of California, San Francisco, California 94143

The formation of sister chromatid exchanges has been postulated to depend upon the action of DNA repair enzymes. Our experiments with various human cell lines show that the yield of sister chromatid exchanges is within normal limits in both excision-repair-defective and post-replication-repair-defective cells from the autosomal recessive disease, xeroderma pigmentosum. These results indicate that hypotheses invoking known DNA repair processes to account for the recombination of sister chromatids are inadequate and that the exact enzymatic processes are as yet unknown.