CHARACTERIZATION OF THE HELA-CELL SINGLE-STRANDED DNA-DEPENDENT ATPASE DNA HELICASE-II

A single-stranded DNA-dependent ATPase activity, consisting of two sub units of 83 kDa (p90) and 68 kDa (p70), was previously purified from H eLa cells (Vishwanatha, J.K. and Baril, E.F. (1990) Biochem 29, 8753-8 759). Homology of the two subunits of single-stranded DNA-dependent AT Pase with the human Ku protein (Cao et al. (1994) Biochem 33, 8548-855 7) and identity of the Ku protein as the human DNA helicase II (Tuteja et al. (1994) EMBO J. 13, 4991-5001) have been reported recently. Usi ng antisera raised against the subunits of the HDH II, we confirm that the Hela single-stranded DNA-dependent ATPase is the HDH II. Similar to the activity reported for Ku protein, ssDNA-dependent ATPase binds to double-stranded DNA and the DNA-protein complex detected by gel mob ility shift assay consists of both the ATPase subunits. The p90 subuni t is predominantly nuclear and is easily dissociated from chromatin. T he p70 is distributed in cytosol and nucleus, and a fraction of the nu clear p70 protein is found to be associated with the nuclear matrix. B oth the p90 and p70 subunits of the ATPase are present in G(1) and S p hase of the cell cycle and are rapidly degraded in the G(2)/M phase of the cell cycle.