Making sense of chaos: replication and segregation defects in the yeast mcm4Chaos3 mutant

In Saccharomyces cerevisiae, the mcm4Chaos3 allele selectively impairs origin firing at early S-phase origins, with the strongest defects at centromere-proximal sites.

• Why it matters: Genome instability depends on replication timing and fidelity, and mcm4Chaos3 was linked to micronuclei and tumorigenesis in mice, but its mechanism was unclear.
• What they did: The study tested mcm4Chaos3 in yeast and measured origin activity and chromosome loss, focusing on chromosome V with centromere-adjacent ARS510 and comparing it to ARS305.
• The result: Chromosome V loss rates were elevated with ARS510 and were rescued by replacing ARS510 with the robust early-firing origin ARS305, restoring origin activity and chromosome stability.

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