Making sense of eukaryotic DNA replication origins

DNA replication is the process by which cells make one complete copy of the ir genetic information before cell division. In bacteria, readily identifia ble DNA sequences constitute the start sites or origins of DNA replication. In eukaryotes, replication origins have been difficult to identify. In som e systems, any DNA sequence can promote replication, but other systems requ ire specific DNA sequences. Despite these disparities, the proteins that re gulate replication are highly conserved from yeast to humans. The resolutio n may lie in a current model for once-per-cell-cycle regulation of eukaryot ic replication that does not require defined origin sequences. This model i mplies that the specification of precise origins is a response to selective pressures that transcend those of once-per-cell-cycle replication, such as the coordination of replication with other chromosomal functions. Viewed i n this context, the locations of origins may be an integral part of the fun ctional organization of eukaryotic chromosomes.