Essential protein (PubMed:15020747). Component of the origin recognition complex (ORC) that binds origins of replication. DNA-binding is ATP-dependent, however specific DNA sequences that define origins of replication have not been identified so far. ORC is required to assemble the pre-replication complex necessary to initiate DNA replication (By similarity). Component of the origin recognition complex (ORC) composed of at least ORC1 (ORC1A or ORC1B), 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. Interacts directly with ORC1A, ORC1B, ORC3, ORC4, ORC5 and ORC6. A number of isoforms are produced. According to EST sequences. Expressed in female gametophyte and embryos, and, at low levels, in trichomes, pollen and the mesophyll of leaves. Follow a cell-cycle regulation with a peak at the G1/S-phase (PubMed:16179646). Mostly expressed in siliques, flowers, flower buds and leaves, and, to a lower exent, in roots and stems (PubMed:16179646, PubMed:15358564). Detected in the mature female gametophyte, in the synergids and central cell. Mostly expressed in embryos (but not the suspensor) and endosperm of preglobular stage seeds. Present in pollen as well as in pollen tubes. Regulated by E2F (PubMed:16179646). Accumulates rapidly after cell cycle reactivation by sucrose addition following cell cycle arrest mediated by sucrose deprivation (PubMed:16179646, PubMed:15358564). Zygotic lethal mutant phenotype. Seeds abort early, with embryos made of up to eight cells, characterized by enlarged nuclei in endosperm with arrested cell cycle. These phenotypes are partly suppressed by mutation in MEA/MEDEA. Belongs to the ORC2 family.