Identification and Characterisation of Proteins Binding to a G-Quadruplex Origin G-rich Repeated Element in Mammalian Cells

Abstract In metazoan cells, replication of genomic DNA initiates from thousands of discrete chromosomal loci known as origins. Proteins such as the Origin Recognition Complex (ORCs) associate with origins, but this does not show clear sequence specificity for DNA binding. Genome-wide origin mapping studies have shown that the region surrounding the replication initiation site contains motifs such as the Origin G-rich Repeated Element (OGRE), proximal to the majority of origins. Here, using an approach coupling DNA affinity purification to quantitative proteomics, we identified proteins that interact specifically with an OGRE. Three of the top-scoring interactors, Dhx36, Pura and Tial1, were selected for further study. We show that Dhx36 and Tial1 localise to the nucleus and their knockdown decreased cells in S-phase resulting in their accumulation in the G 1 phase of the cell cycle. Altogether these results indicate that these OGRE-binding factors may play roles in DNA synthesis in mammalian cells.