Studies with yeast and Xenopus have provided evidence that the beginning of DNA replication is a multistep process. Prereplication complexes must be established before cyclin-dependent kinases and the Dbf4p-dependent kinase Cdc7p can initiate replication. These proteins are the origin recognition complex (ORC), Cdc6p, and mini-chromosome maintenance (MCM). Investigation of S-phase control in mammalian cells is made possible by the discovery of these replication proteins' human homologues.
We show that whereas human Orc2 (hOrc2p) and human Mcm proteins are present throughout the cell cycle, hCdc6p levels fluctuate, being very low in early G(1) and building up until cells enter mitosis using centrifugal elutriation of numerous human cell lines.
<h3>What is Chromatin ?</h3>
Each DNA molecule that is attached to a histone protein is referred to as a chromosome, and this combination is known as chromatin. However, chromatin also regulates how the genome is read out from cell to cell and compacts the genome into the nucleus.
Numerous cellular functions, including DNA replication, transcription, DNA repair, genetic recombination, and cell division, are made possible by chromatin.
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