Evolution of Origin Sequence and Recognition for Licensing of Eukaryotic DNA Replication

The large size of eukaryotic chromosomes necessitates that the initiation of DNA replication occurs at numerous origins of DNA replication. In S. cerevisiae, origins are highly DNA sequence-specific and are recognized by the Origin Recognition Complex (ORC). In contrast, most eukaryotes lack features in ORC subunits that contribute to DNA sequence-specific recognition, raising the question of how origins are identified. An analysis of origins in the genome of the distantly related budding yeast Yarrowia lipolytica identified considerable variability in origin sequence and structure. High-resolution structures demonstrate that Y. lipolytica origins are recognized by a combination of ORC and Cdc6 in a manner different from S. cerevisiae. The structure of Yarrowia ORC-Cdc6 bound to different origins shows considerable plasticity in protein-DNA interactions. We compare these yeast structures to the structure of human ORC-CDC6 bound to DNA. These studies reveal information on the evolution of origins and origin recognition. Nomenclature note: There is a different nomenclature for proteins in yeast and human cells. For example, Cdc6 in yeasts is CDC6 in human cells.