UV LIGHT-INDUCED DNA-SYNTHESIS ARREST IN HELA-CELLS IS ASSOCIATED WITH CHANGES IN PHOSPHORYLATION OF HUMAN SINGLE-STRANDED DNA-BINDING PROTEIN

We show that DNA replication activity in extracts of human HeLa cells decreases following UV irradiation. Alterations in replication activit y in vitro parallel the UV-induced block in cell cycle progression of these cells in culture. UV irradiation also induces specific changes i n the pattern of phosphorylation of the 34 kDa subunit of a DNA replic ation protein, human single-stranded DNA-binding protein (hSSB). The a ppearance of a hyperphosphorylated form of hSSB correlates with reduce d in vitro DNA replication activity in extracts of UV-irradiated cells . Replication activity can be restored to these extracts in vitro by a ddition of purified hSSB. These results suggest that UV-induced DNA sy nthesis arrest may be mediated in part through phosphorylation-related alterations in the activity of hSSB, an essential component of the DN A replication apparatus.