Disease relevance of ORC2L

• Cells carrying this mutation failed to support the replication of a plasmid bearing the oriP replicator of Epstein Barr virus (EBV), and this defect was rescued by reintroduction of Orc2 [1].

High impact information on ORC2L

• A hypomorphic mutation made in the ORC2 gene of a human cancer cell line through homologous recombination decreased Orc2 protein levels by 90% [1].
• Moreover, the BAH domain affected Orc1's ability to promote binding of Orc2 to chromatin as cells exit mitosis [2].
• In human cells, the Orc2 subunit localized to the nucleus as expected, but it also localized to centrosomes throughout the entire cell cycle [3].
• Human Orc2 localizes to centrosomes, centromeres and heterochromatin during chromosome inheritance [3].
• These results implicate Orc2 protein in chromosome duplication, chromosome structure and centrosome copy number control, suggesting that it coordinates all stages of the chromosome inheritance cycle [3].

Biological context of ORC2L

• Consistent with a role of CDC45L protein in the initiation of DNA replication it co-immunoprecipitates from cell extracts with a putative replication initiator protein, human ORC2L [4].
• Analyses of somatic cell hybrid DNA and fluorescence in situ hybridization were employed to map the human ORC2L gene to chromosome 2q33 [5].
• Cdc6 binding mirrored that of Orc2 in G(1)-arrested cells but decreased in asynchronous or M-phase cells [6].
• Here we use two different approaches to investigate the presence of the human ORC2 protein and of Mcm proteins on chromatin of HeLa cells in various cell cycle phases [7].
• Under digestion conditions when Mcm proteins were almost entirely released from chromatin, ORC2 protein was found to be associated with chromatin fragments containing several hundred base pairs of DNA [7].

Anatomical context of ORC2L

• To study the assembly and function of mammalian ORC proteins in their native environment, HeLa cells were constructed that constitutively expressed an epitope-tagged, recombinant human Orc2 subunit that had been genetically altered [8].

Associations of ORC2L with chemical compounds

• Previously shown to cause histone hyperacetylation and delocalization of replication initiation, trichostatin A treatment of cells led to a parallel qualitative change in the distribution of Mcm3, but not Orc2, across the c-myc replicator [6].
• Second, we used an in vivo cross-linking procedure to covalently link Mcm proteins and ORC2 to DNA by short exposure of intact HeLa cells to formaldehyde [7].
• Molecular combing of bromodeoxyuridine-labeled DNA revealed that once the Orc2 hypomorphic cells enter S-phase, fork density and fork progression are approximately comparable with wild type cells [9].
• Two isoforms of the human ornithine carrier, ORC1 and ORC2, have been identified by overexpression of the proteins in bacteria and by study of the transport properties of the purified proteins reconstituted into liposomes [10].

Physical interactions of ORC2L

• Furthermore, Orc2 was tightly bound to heterochromatin and heterochromatin protein 1alpha (HP1alpha) and HP1beta in G1 and early S phase, but during late S, G2 and M phases tight chromatin association was restricted to centromeres [3].

Regulatory relationships of ORC2L

• We have previously reported generation of an Orc2 hypomorph cell line (Delta/-) that expresses very low levels of Orc2 but is viable [9].

Other interactions of ORC2L

• The precise nucleotide of binding was identified for the two ORC and the CDC6 proteins near the start sites for leading-strand synthesis; the transition from the pre- to the post-replicative complex is accompanied by a 17 bp displacement of the ORC2 protein towards the start site [11].
• Therefore, the low level of Orc2 hinders normal cell cycle progression by delaying the activation of G1 cyclin-dependent kinases [9].
• These results demonstrate an unexpected role of ORC2 in CDK2 activation, a linkage that could be important for maintaining genomic stability [12].
• Sequences corresponding to the intergenic region are highly abundant in a fraction of nascent DNA strands, strongly suggesting that this region not only harbors the binding sites for Orc1 protein and Orc2 protein but also serves as an origin of bidirectional DNA replication [13].
• Cellular extraction revealed that the proportion of ORC2 and ORC4 subunits bound to chromatin was similar in all three cell lines throughout the cell-cycle [14].

Analytical, diagnostic and therapeutic context of ORC2L

• Specific immunoprecipitations revealed that cross-linked nucleoprotein fragments carried either Mcm proteins or ORC2 protein, but not both [7].
• A quantitative chromatin immunoprecipitation (ChIP) assay, using antibodies against Ku, Orc2, and Cdc6, showed that these DNA replication initiator proteins were associated in vivo with the human ors8 (hors8) [15].
• Using the yeast two-hybrid system and immunoprecipitation, we report here that murine HP1alpha interacts with the preRC proteins ORC1, ORC2 and CDC6 [16].
• Sequence alignment shows that there is a high homology between the deduced amino sequence of OsORC2 and maize ORC2 (85%) [17].

References