In yeast, the combined action of Cdc6, Cdtl, and the MCM proteins provides the licensing function.

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#Unit 3. Fundamental Processes

oriC also contains 11 GATC/CTAG repeats that are methylated on adenine on both strands.

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#Unit 3. Fundamental Processes

Before replication, the palindromic target GATC site is methylated by dam methylase on the N6 of A of each strand.

Replication generates hemimethylated DNA, in which one strand is methylated and one strand is unmethylated.

Thus, the replication event converts Dam target sites from fully methylated to hemimethylated condition.

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Dam (Dam-) mutants accumulates hemimethylated products after replication.

If the plasmid is methylated, it undergoes a single round of replication, and then the hemimethylated products accumulate.

Suggesting that a hemimethylated origin cannot be used to initiate a replication cycle.

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Only fully methylated origins can initiate replication;

hemimethylated daughter origins cannot be used again until they have been restored to the fully methylated state.

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The GATC sites AT THE ORIGIN remain hemimethylated for 13 minutes after replication called as refractory period of replication cycle or delay time.

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At typical GATC sites elsewhere in the genome, remethylation begins immediately (1.5 minutes) following replication.