Abnormality in DNA-protein binding in ataxia-telangiectasia nuclear extracts

Evidence of different complementation groups amongst human genetic disorders characterized by radiosensitivity

The genetic diversity of a clinically heterogeneous group of ionizing radiation-sensitive human mutants has been examined. In this group, the relationship between ataxia telangiectasia (A-T), Alzheimer's disease (AD) and Down's syndrome (DS) was studied, on the basis of their cellular radiosensitivity. Cell-fusion analysis was used to determine the presence of different complementation groups. In a series of 4A-T, 5AD and 4DS cell lines, 8 complementation groups were documented. These findings suggest that this group of primary neuronal degenerative disorders might have some overlap in their genetic defects.

Modification of deoxyribose-phosphate residues by extracts of ataxia telangiectasia cells

The release of DNA 5'-terminal deoxyribose-phosphate residues from enzymatically incised apurinic/apyrimidinic sites by human cell extracts has been under investigation. During the course of these studies, we observed that ataxia telangiectasia cell extracts modify deoxyribose-phosphate (dRp) residues by converting them to an altered form, dRp-X, which shows altered chromatographic properties on HPLC analysis. The chemical nature of the adduct is as yet unknown, but dRp-X is stable to both heat and acid. The modification requires an enzymatic activity and a low-molecular weight co-factor. Extracts of normal cells contain a dialyzable inhibitor that suppresses the reaction occurring with ataxia telangiectasia cell extracts. Formation of dRp-X has been observed in 7 out of 7 ataxia telangiectasia lymphoblastoid lines which represent at least 3 genetic complementation groups. Similar modification of dRp did not occur with extracts of cells of normal origin, nor those representing Fanconi's anaemia, xeroderma pigmentosum, Bloom's syndrome, Werner's syndrome or Friedreich's ataxia.