Essential protein (By similarity). Component of the origin recognition complex (ORC) that binds origins of replication. It has a role in both chromosomal replication and mating type transcriptional silencing. Binds to the ARS consensus sequence (ACS) of origins of replication (By similarity). H3K4me3 effector that regulates positively the transcription of a subset of genes (By similarity). Required for cell proliferation (PubMed:10996242). Component of the origin recognition complex (ORC) composed of at least ORC1, ORC2, ORC3, ORC4, ORC5 and ORC6. ORC is regulated in a cell-cycle and development dependent manner. It is sequentially assembled at the exit from anaphase of mitosis and disassembled as cells enter S phase (By similarity). Binds unmodified and methylated histone H3 (By similarity). Expressed strongly in root tips and shoot apical meristem (SAM), and weakly in young leaves. Not detected in mature leaves. Reduced expression upon sucrose depletion-mediated cell proliferation arrest, and accumulates after sucrose treatment (PubMed:10996242, PubMed:15939553). Induced by gamma irradiation (PubMed:25124817). Belongs to the ORC1 family.