Components
As organisms evolved and became increasingly more complex, so did their pre-RCs. The following is a summary of the components of the pre-RC amongst the different domains of life.
In prokaryotes, the main component of the pre-RC is DnaA. The pre-RC is complete when DnaA occupies all of its binding sites within the prokaryotic origin of replication (oriC).
The archaeal pre-RC is very different from the prokaryotic pre-RC and can serve as a simplified model of the eukaryotic pre-RC. It is composed of a single origin recognition complex (ORC) protein, Cdc6, and a homohexamer of the Mini Chromosome Maintenance (MCM) protein.
The eukaryotic pre-RC is the most complex and highly regulated pre-RC. In most eukaryotes it is composed of six ORC proteins (ORC1-6), Cdc6, Cdt1, and a heterohexamer of the six MCM proteins (MCM2-7). The MCM heterohexamer arguably arose via MCM gene duplication events and subsequent divergent evolution. The pre-RC of Schizosaccharomyces pombe (S. pombe) is notably different from that of other eukaryotes; Cdc6 is replaced by the homologous Cdc18 protein. Sap1 is also included in the S. pombe pre-RC because it is required for Cdc18 binding. The pre-RC of Xenopus laevis (X. laevis) also has an additional protein, MCM9, which helps load the MCM heterohexamer onto the origin of replication.
Read more about this topic: Pre-replication Complex
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