A DUE serves to facilitate the opening of the double helix during initiation of replication. DUE mutations that stabilize the double helix in vitro lead to impairment or inactivation of the replication origin in living cells. In E. coli oriC and in the SV40 ori, the DUE identified by analysis of mutations in vivo occurs at the same site that the replication initiator protein induces to unwind in vitro. Yeast is helping us to understand how DNA replication is regulated in cell chromosomes. Despite the simplicity of the organism, enzymes and proteins from yeast often exhibit structures and functions similar to enzymes and proteins from cells of multicellular organisms, even humans.
Yeast offers the advantage of being highly amenable to genetic manipulation and analysis.
Yeast replication origins can be isolated from the chromosome, inserted into plasmids, and easily studied using a genetic marker to track plasmid inheritance in dividing cells. We have identified multiple DNA elements that contribute to plasmid inheritance. More remains to be learned about the factors that govern activation of replication origins within chromosomes. The locations of replication origins in a yeast chromosome are not predictable using the available information. More studies need to be done in the context of chromosomes, where replication origins are subject to interference by other origins, to specific temporal regulation, to possible transcriptional regulation and to a particular nuclear localization and chromatin structure.