The origin recognition complex (ORC) is a highly conserved heterohexameric protein complex that associates with DNA at or near initiation of DNA replication sites.

All six ORC subunits are essential for initiation of DNA replication (1-3), and ORC may be involved in regulation of gene expression in response to stress (4).

Most of our knowledge about initiation of eukaryotic DNA replication are derived from the study of budding yeast Saccharomyces cerevisiae.