DUE-B, A NEW HUMAN DNA REPLICATION PROTEIN, IS THE FUNCTIONAL HOMOLOG OF S. CEREVISIAE SLD3

by Yao, Jianhong

DNA unwinding elements (DUEs) are commonly found at DNA replication origins. The DUE binding protein (DUE-B) is crucial for the initiation of DNA replication in eukaryotes. The unique 59 amino acid C-terminal part of DUE-B shares nearly 50% similarity with yeast the C-terminus of Sld3. DUE-B plays a key role in eukaryotic DNA replication because it is required for the loading of Cdc45, the MCM helicase activator, on chromatin. Here we show that DUE-B, just like yeast Sld3, binds to Cdc45 and TopBP1 through its C-terminus in Sf9 cells and in vitro. We also show that DUE-B, Cdc45 and TopBP1 form a heterotrimeric complex in vitro. The mass spectrometric data show that dominant negative Sf9 DUE-B is not phosphorylated but functional HeLa DUE-B is phosphorylated. All these data suggest that human DUE-B is a functional homolog of yeast Sld3.