A deficiency in a 230 kDa DNA repair protein in Fanconi anemia complementation group A cells is corrected by the FANCA cDNA

Cells from individuals with the cancer-prone, inherited disorder Fanconi an emia (FA) are hypersensitive to DNA interstrand cross-linking agents and th is hypersensitivity correlates with a defect in ability to repair this type of damage to their DNA, We have isolated a DNA endonuclease complex from t he nuclei of normal human cells which is involved in repair of DNA interstr and cross-links and have shown that in FA complementation group A (FA-A) ce lls there is a defect in ability of this complex to incise DNA containing i nterstrand cross-links. In order to identify the specific protein(s) in thi s complex which is defective in FA-A cells, monoclonal antibodies (mAbs) we re developed against proteins in the normal complex. One of these mAbs, whi ch is against a protein with a molecular weight of similar to 230 kDa, comp letely inhibited the ability of the normal complex to incise cross-linked D NA, Western blot analysis has shown that there is a deficiency in this prot ein in FA-A cells. Electophoretic analysis has also indicated that there ar e reduced levels of this protein in FA-A compared with normal cells, Studie s carried out utilizing FA-A cells which have been stably transduced with a retroviral vector expressing the FANCA cDNA have shown that the DNA repair defect in these cells has been corrected; levels of unscheduled DNA synthe sis are at least as great as those of normal human cells. In addition, in t he transduced cells the deficiency in the 230 kDa protein has been correcte d, as determined by both western blot and electrophoretic analysis. These r esults indicate that the FANCA gene plays a role in the expression or stabi lity of the 230 kDa protein.