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

Abstract

Saccharomyces cerevisiae has been a faithful guide for study of eukaryotic DNA replication, as the numerous initiation and elongation proteins are conserved from yeast to human. However, there is a gap in our knowledge of why yeast uses a consensus DNA sequence at replication origins, while higher eukaryotes do not. The current study closes this gap. By direct single-molecule visualization, we show that the Origin Recognition Complex (ORC) searches for and stably binds nucleosomes, and that nucleosomes funtionalize ORC to load MCM helicase onto DNA, regardless of DNA sequence. Furthermore, we discover that ORC can remodel nucleosomes and expel H2A-H2B histone dimers, a heretofore unexpected function. Thus ORC helps create a chromatin environment permissive to origin function. The finding that ORC binding to nucleosomes leads to MCM loading at any DNA sequence is likely to generalize, and that higher eukaryotes follow this same paradigm for origin selection.

Establishment and Function of Chromatin Architecture at Eukaryotic Chromosome Replication Origins

“…It is possible that ORC uses ATP hydrolysis to actively manipulate chromatin structure. Supporting this idea, recent work showed that ORC can evict H2A-H2B dimers 33 .…”