Identification and Characterization of cis-acting DNA Elements that Regulate Early Origin Activation

Abstract

Duplication of a cell's genome is a central requirement for the propagation of life. This duplication, a highly regulated process known as DNA replication, occurs in S-phase and is initiated at genomic sites termed origins of replication (origins). In eukaryotes, origins are activated (initiate DNA synthesis) on average at different times in S-phase; some are activated in early S-phase while others are activated in late S-phase. This variation in origin activation time allows the genome to be replicated in a temporally staggered fashion. The biological significance and mechanisms behind temporal DNA replication have remained largely elusive. In the budding yeast <italic>Saccharomyces cerevisiae</italic>, the activation times of individual origins are not intrinsic to those origins but instead are governed by surrounding sequences and their local chromatin environment. My research, presented in this dissertation, identifies and characterizes DNA sequences in yeast that function to advance origin activation time. Through this work, I show that centromeres ensure their own early replication by inducing early activation of pericentric origins. I propose and investigate the hypothesis that there is selective pressure to replicate centromeres in early S-phase. Furthermore, I have also helped to provide evidence for the existence of centromere independent mechanisms that promote early origin activation.