Analyzing origin activation patterns by copy number change experiments

Advances in microarray technology have enabled the analysis of replication dynamics on a genome-wide scale, providing deeper insight to the factors that regulate DNA replication. Studies using high-density microarrays have led to the genome-wide identification of replication origins in the budding yeast, Saccharomyces cerevisiae, and enabled the analysis of the global temporal pattern of origin activation under various conditions. We have developed a replication origin array that contains the ~430 potential origins in the yeast genome. By detecting the copy number change that occurs as cells progress from G1 to S phase on these arrays, we have produced origin activation patterns in wild-type cells similar to those obtained from previous studies that used whole-genome arrays. We have also applied this method to study S phase checkpoint mutants, providing insight into the genome-wide regulation of replication origin activation by S phase checkpoint kinases in the presence of replication stress. The main procedures of this technique involve arresting yeast cells in G1 and S phase, isolating and labeling genomic DNA with fluorescent dyes, and cohybridizing the DNA samples to replication origin arrays to yield copy number change data.