Eukaryotic DNA Replication

Although not as well understood, eukaryotic replication resembles bacterial replication in many respects. The most obvious differences are that eukaryotes have: (1) multiple replication origins in their chromosomes; (2) more types of DNA polymerases, with different functions; and (3) nucleosome assembly immediately following DNA replication.

Eukaryotic origins Researchers first isolated eukaryotic origins of replication from yeast cells by demonstrating that certain DNA sequences confer the ability to replicate when transferred from a yeast chromosome to small circular pieces of DNA (plasmids). These autonomously replicating sequences (ARSs) enabled any DNA to which they were attached to replicate. They were subsequently shown to be the origins of replication in yeast chromosomes.

Yeast ARSs typically consist of 100 to 120 bp of DNA. A multiprotein complex, the origin recognition complex (ORC), binds to the ARS and probably unwinds the DNA in this region. Interestingly, ORCs also function in regulating transcription. __

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