Investigation of the Interaction of Human Origin Recognition Complex Subunit 1 with G-Quadruplex DNAs of Human Promoter and Telomere Regions.

Origin recognition complex (ORC) binds to replication origins in eukaryotic DNAs and plays an important role in replication. Although yeast ORC is known to sequence-specifically bind to a replication origin, how human ORC recognizes a replication origin remains unknown. Previous genome-wide studies revealed that guanine (G)-rich sequences, potentially forming G-quadruplex (G4) structures, are present in most replication origins in human cells. We previously suggested that the region comprising residues 413-511 of human ORC subunit 1, hORC1, binds preferentially to G-rich DNAs, which form a G4 structure in the absence of hORC1. Here, we investigated the interaction of hORC1 with various G-rich DNAs derived from human promoter and telomere regions. Fluorescence anisotropy revealed that hORC1 binds preferentially to DNAs that have G4 structures over ones having double-stranded structures. Importantly, circular dichroism (CD) and nuclear magnetic resonance (NMR) showed that those G-rich DNAs retain the G4 structures even after binding with hORC1. NMR chemical shift perturbation analyses revealed that the external G-tetrad planes of the G4 structures are the primary binding sites for hORC1. The present study suggests that human ORC1 may recognize replication origins through the G4 structure.