Nucleosome-directed replication origin licensing independent of a consensus DNA sequence (Li et al., Nat Commun 2022)
ARS-directed origin licensing exclusively found in budding yeast vs. nucleosome-directed origin licensing potentially applicable to all eukaryotes.
The numerous enzymes and cofactors involved in eukaryotic DNA replication are conserved from yeast to human, and the budding yeast Saccharomyces cerevisiae (S.c.) has been a useful model organism for these studies. However, there is a gap in our knowledge of why replication origins in higher eukaryotes do not use a consensus DNA sequence as found in S.c. Using in vitro reconstitution and single-molecule visualization, we in collaboration with the O’Donnell Lab show that S.c. origin recognition complex (ORC) stably binds nucleosomes and that ORC-nucleosome complexes have the intrinsic ability to load the replicative helicase MCM double hexamers onto adjacent nucleosome-free DNA regardless of sequence. Combined with re-analysis of genome-wide S.c. ORC binding data performed by the Bai Lab, our results lead us to propose that S.c. ORC contains the cryptic capacity to license origins next to nucleosome sites and this nucleosome-directed origin licensing paradigm generalizes to all eukaryotes.