Choreography of Eukaryotic DNA Replication

PROJECT SUMMARY Faithful replication of the genome is a core mission of all dividing cells. Accordingly, cells have evolved mechanisms to monitor replication fidelity and to coordinate completion of replication with other cell cycle events. In eukaryotes, chromosome replication is initiated at multiple initiation sites (origins), which are a key target of the cell’s regulatory mechanisms ensuring proper genome maintenance. Cells can regulate origin choice (which potential origins they use), efficiency (how likely they are to use it in any given cell cycle), and initiation time, to choreograph the overall duplication of the genome. Disruption of this choreography has been linked to a variety of human disorders including cancer. Although origins are not conserved at the sequence level, the protein machinery is highly conserved, allowing discovery of key aspects of these fundamental processes in simple models such as Baker’s yeast because of its small chromosomes, well defined origin sequences, ease of altering chromosome structure, and exceptional systems for genetic and genomic analysis. A recent discovery is the key role played by the rDNA—the locus containing tandemly-repeated copies of ribosomal RNA genes—in modulating genome duplication and maintenance. Over the next five years, this project will investigate how the choreography of chromosome replication is established and why it is so important in eukaryotes: How is rDNA replication regulated, and how does rDNA copy number affect genome stability? How are origin preference and replication timing determined genome-wide? And how do alterations in the choreography of genome replication contribute to phenotypes such as those seen in human disorders?