COMPLEMENTATION OF THE DNA-REPAIR DEFECT IN XERODERMA-PIGMENTOSUM GROUP-G CELLS BY A HUMAN CDNA RELATED TO YEAST RAD2

DEFECTS in human DNA repair proteins can give rise to the autosomal re cessive disorders xeroderma pigmentosum (XP) and Cockayne's syndrome ( CS), sometimes even together1-3. Seven XP and three CS complementation groups have been identified that are thought to be due to mutations i n genes from the nucleotide excision repair pathway2,3. Here we isolat e frog and human complementary DNAs that encode proteins resembling RA D2, a protein involved in this pathway in yeast4,5. Alignment of these three polypeptides, together with two other RAD2 related proteins6,7, reveals that their conserved sequences are largely confined to two re gions. Expression of the human cDNA in vivo restores to normal the sen sitivity to ultraviolet light and unscheduled DNA synthesis of lymphob lastoid celts from XP group G, but not CS group A. The XP-G correcting protein XPGC is generated from a messenger RNA of approximately 4 kil obases that is present in normal amounts in the XP-G cell line.