PRESENCE OF HUMAN CELLULAR PROTEIN(S) THAT SPECIFICALLY BINDS AND CLEAVES 8-HYDROXYGUANINE CONTAINING DNA

8-hydroxyguanine (oh(8)Gua) is a major form of oxygen free radical-ind uced DNA damage. The oh(8)Gua nucleotide can pair with cytosine (C) an d adenine (A) nucleotides which can cause G:C to T:A transversions. It is known that multiple repair systems for the correction of the oh(8) Gua exist in both mammalian and bacterial cells. Using the technique o f gel mobility shift assay, protein(s) bound to the oh(8)Gua:C base pa ir in short fragments of DNA was detected in cell-free extracts of a h uman small-cell lung cancer cell line. This DNA binding activity was s pecific, since it was poorly detected with an unmodified G:C base pair containing oligonucleotide duplex and was affected by neither the unm odified G:C base pair nor an oh(8)Gua:A base pair containing oligonucl eotide duplex. The partially purified protein which selectively binds to the oh(8)Gua:C base pair was shown by gel filtration column chromat ography to have an apparent molecular mass of 52 kDa. The column fract ion which showed the highest binding activity to the oh(8)Gua:C base p air was found to possess an enzymatic activity that specifically cleav es the oh(8)Gua containing oligonucleotide strand at both the 5' and 3 ' sides of the oh(8)Gua residue. These results indicate the presence o f a protein(s) that is involved in a DNA repair pathway for the correc tion of the oh(8)Gua residue in human cells.