Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Origin recognition complex
open-in-new
<p>In <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a>, origin recognition complex (ORC) is a multi-subunit <a href="/facts/DNA/nB89Iauz">DNA</a> binding complex (6 subunits) that binds in all <a href="/facts/Eukaryotes/SkwyPLMA">eukaryotes</a> and <a href="/facts/Archaea/Adxh0aHw">archaea</a> in an <a href="/facts/Adenosine_triphosphate/nB9bwgcU">ATP</a>-dependent manner to <a href="/facts/Origins_of_replication/StuSWefk">origins of replication</a>. The subunits of this complex are encoded by the <a href="/facts/ORC1/mwvRPSw6">ORC1</a>, <a href="/facts/ORC2L/oa4Mw8yz">ORC2</a>, <a href="/facts/ORC3L/uRmdBIpr">ORC3</a>, <a href="/facts/ORC4L/fot6cfcj">ORC4</a>, <a href="/facts/ORC5L/59T60ey1">ORC5</a> and <a href="/facts/ORC6L/qKI3bcfk">ORC6</a> genes. ORC is a central component for <a href="/facts/Eukaryotic_DNA_replication/TEqVcIH9">eukaryotic DNA replication</a>, and remains bound to <a href="/facts/Chromatin/ha0TJheJ">chromatin</a> at <a href="/facts/Self_replication/NbsfzT4l">replication</a> origins throughout the <a href="/facts/Cell_cycle/nLMT7K4r">cell cycle</a>. </p><p>ORC directs <a href="/facts/DNA_replication/wrU6RuR3">DNA replication</a> throughout the <a href="/facts/Genome/31Sm08JT">genome</a> and is required for its initiation. ORC and Noc3p bound at replication origins serve as the foundation for assembly of the <a href="/facts/Pre-replication_complex/4jdpMYQa">pre-replication complex</a> (pre-RC), which includes <a href="/facts/Cdc6/va3lPJdC">Cdc6</a>, Tah11 (a.k.a. <a href="/facts/Cdt1/XjmlMxgX">Cdt1</a>), and the <a href="/facts/MCM2/jr3Hyc8T">Mcm2</a>-<a href="/facts/MCM7/Tw5pQE12">Mcm7</a> complex. Pre-RC assembly during <a href="/facts/G1_phase/92lq1LdT">G1</a> is required for replication <a href="/facts/Licensing_factor/RHWLW6QE">licensing</a> of <a href="/facts/Chromosomes/FRGf11FC">chromosomes</a> prior to DNA synthesis during <a href="/facts/S_phase/vplz8LTU">S phase</a>. Cell cycle-regulated <a href="/facts/Phosphorylation/LXUEEeIL">phosphorylation</a> of Orc2, Orc6, Cdc6, and MCM by the <a href="/facts/Cyclin/XtodJmQa">cyclin</a>-dependent <a href="/facts/Protein_kinase/U4DQVhW3">protein kinase</a> <a href="/facts/Cdc28/QEf7kgbm">Cdc28</a> regulates initiation of DNA replication, including blocking reinitiation in <a href="/facts/G2_phase/alNtT0m1">G2</a>/<a href="/facts/M_phase/nLMT7K4r">M phase</a>. </p><p>The ORC is present throughout the cell cycle bound to replication origins, but is only active in late <a href="/facts/Mitosis/ExxrSUs8">mitosis</a> and early <a href="/facts/G1_phase/92lq1LdT">G1</a>. </p><p>In yeast, ORC also plays a role in the establishment of silencing at the <a href="/facts/Mating_of_yeast/tsfekjnJ">mating-type</a> <a href="/facts/Locus_(genetics)/JcIT8wLm">loci</a> Hidden MAT Left (HML) and Hidden MAT Right (HMR). ORC participates in the assembly of <a href="/facts/Transcription_(genetics)/bDgp9HDN">transcriptionally</a> silent <a href="/facts/Chromatin/ha0TJheJ">chromatin</a> at HML and HMR by recruiting the Sir1 silencing <a href="/facts/Protein/Jxmagu3E">protein</a> to the HML and HMR silencers. </p><p>Both Orc1 and Orc5 bind ATP, though only Orc1 has <a href="/facts/ATPase/8aEJlNgl">ATPase</a> activity. The <a href="/facts/Binding_(molecular)/cBnorUC5">binding</a> of ATP by Orc1 is required for ORC binding to DNA and is essential for cell viability. The ATPase activity of Orc1 is involved in formation of the pre-RC. ATP binding by Orc5 is crucial for the stability of ORC as a whole. Only the Orc1-5 <a href="/facts/Protein_subunit/HhuET9UP">subunits</a> are required for origin binding; Orc6 is essential for maintenance of pre-RCs once formed. Interactions within ORC suggest that Orc2-3-6 may form a core complex. A 2020 report suggests that budding yeast ORC dimerizes in a cell cycle dependent manner to control licensing. </p>