URACIL DNA-GLYCOSYLASE GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE IS ANAP(4)A BINDING-PROTEIN

A 37 kDa protein that binds to diadenosine tetraphosphate (Ap(4)A) was purified from human HeLa cells and identified as uracil DNA glycosyla se/glyceraldehyde-3-phosphate dehydrogenase (UDG/GAPDH). Utilizing pho toaffinity labeling with [alpha-P-32]8N(3)-Ap(4)A, an Ap(4)A binding p rotein of 37 kDa was identified from HeLa cell nuclear extracts. The 3 7 kDa protein was purified to homogeneity and subjected to trypsin dig estion followed by amino acid sequence analysis. Two peptide sequences were determined and both had complete identity with the amino acid se quence of the 37 kDa polypeptide of UDG/GAPDH. Purified UDG/GAPDH bind s to Ap(4)A with the same affinity as the HeLa cell nuclear 37 kDa Ap( 4)A binding protein, and monoclonal antibodies to UDG/GAPDH cross-reac t with the 37 kDa Ap(4)A binding protein. UDG/GAPDH has been previousl y demonstrated to have numerous nonglycolytic activities. The UDG func tion is involved in DNA repair by excision of uracil from DNA. GAPDH i s a RNA binding protein and binds to tRNA and AU-rich RNA. The AU-rich RNA binding has been implicated in the regulation of AU-rich element dependent mRNA turnover and translation. The identification of UDG/GAP DH as an Ap(4)A binding protein may be physiologically relevant to the proposed role of Ap(4)A as a regulatory nucleotide in cell growth.