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General Comment |
NCBI Summary:
The origin recognition complex (ORC) is a highly conserved six subunits protein complex essential for the initiation of the DNA replication in eukaryotic cells. Studies in yeast demonstrated that ORC binds specifically to origins of replication and serves as a platform for the assembly of additional initiation factors such as Cdc6 and Mcm proteins. The protein encoded by this gene is a subunit of the ORC complex. This protein forms a core complex with ORC3, -4, and -5. It also interacts with CDC45 and MCM10, which are proteins known to be important for the initiation of DNA replication. This protein has been demonstrated to specifically associate with the origin of replication of Epstein-Barr virus in human cells, and is thought to be required for DNA replication from viral origin of replication. Alternatively spliced transcript variants have been found, one of which is a nonsense-mediated mRNA decay candidate. [provided by RefSeq, Oct 2010]
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Comment |
Unique Pattern of ORC2 and MCM7 Localization During DNA Replication Licensing in the Mouse Zygote. Ortega MA et al. In eukaryotes, DNA synthesis is preceded by licensing of replication origins. We examined the subcellular localization of two licensing proteins, ORC2 and MCM7, in the mouse zygotes and 2-cell embryos. In somatic cells ORC2 remains bound to DNA replication origins throughout the cell cycle, while MCM7 is one of the last proteins to bind to the licensing complex. We found that MCM7, but not ORC2 was bound to DNA in metaphase II oocytes, and remained associated with the DNA until S-phase. Shortly after fertilization, ORC2 was detectable at the metaphase II spindle poles, and then between the separating chromosomes. Neither protein was present in the sperm cell at fertilization. As the sperm head decondensed, MCM7 was bound to DNA, but no ORC2 was seen. By four hours after fertilization, both pronuclei contained DNA bound ORC2 and MCM7. As expected, during S-phase of the first zygotic cell-cycle, MCM7 was released from the DNA but ORC2 remained bound. During zygotic mitosis, ORC2 again localized first to the spindle poles, then to the area between the separating chromosomes. ORC2 then formed a ring around the developing 2-cell nuclei before entering the nucleus. Only soluble MCM7 was present in the G2 pronuclei, but by zygotic metaphase it was bound to DNA, again apparently before ORC2. In G1 of the 2-cell stage, both nuclei had salt-resistant ORC2 and MCM7. These data suggest that licensing follows a unique pattern in the early zygote that differs from what has been described for other mammalian cells that have been studied.
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