Nucleosome-directed replication origin licensing independent of a consensus DNA sequence

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Eukaryotic DNA replication involves conserved enzymes and cofactors, with yeast as a model.
• Higher eukaryotes lack consensus DNA sequences at replication origins, unlike yeast.
• The precise mechanism of origin selection in higher eukaryotes remains unclear.

Purpose of the Study:

• To investigate the role of nucleosomes in DNA replication origin licensing.
• To determine if yeast origin recognition complex (ORC) can bind nucleosomes.
• To explore the conservation of nucleosome-directed origin licensing across eukaryotes.

Main Methods:

• In vitro reconstitution assays.
• Single-molecule visualization techniques.
• Re-analysis of genome-wide ORC binding data.

Main Results:

• Yeast ORC stably binds to nucleosomes.
• ORC-nucleosome complexes can load the MCM helicase onto nearby nucleosome-free DNA, irrespective of sequence.
• Nucleosomes from Xenopus laevis can also engage with yeast ORC.
• Genome-wide data support a model of nucleosome-directed origin licensing.

Conclusions:

• The yeast ORC machinery possesses a latent ability to bind nucleosomes and license origins.
• This nucleosome-directed origin licensing paradigm is likely conserved in all eukaryotes.
• Replication origin selection in higher eukaryotes may be guided by nucleosome positioning rather than specific DNA sequences.