The Cockayne Syndrome group B gene product is involved in general genome base excision repair of 8-hydroxyguanine in DNA

Cockayne Syndrome (CS) is a human genetic disorder with two complementation groups, CS-A and CS-B. The CSB gene product is involved in transcription-c oupled repair of DNA damage but may participate in other pathways of DNA me tabolism. The present study investigated the role of different conserved he licase motifs of CSB in base excision repair. Stably transformed human cell lines with site-directed CSB mutations in different motifs within its puta tive helicase domain were established. We find that CSB null and helicase m otif V and VI mutants had greater sensitivity than wild type cells to gamma -radiation. Whole cell extracts from CSB null and motif V/VI mutants had l ower activity of 8-hydroxyguanie incision in DNA than wild type cells. Also , 8-hydroxyguanine accumulated more in CSB null and motif VI mutant cells t han in wild type cells after exposure to gamma -radiation. We conclude that a deficiency in general genome base excision repair of selective modified DNA base(s) might contribute to CS pathogenesis. Furthermore, whereas the d isruption of helicase motifs V or VI results in a CSB phenotype, mutations in other helicase motifs do not cause this effect. The biological functions of CSB in different DNA repair pathways may be mediated by distinct functi onal motifs of the protein.