Replication origins in yeast versus metazoa: separation of the haves and the have nots.

The recent flood of information concerning Saccharomyces cerevisiae replication origins and the proteins that interact with them contrasts alarmingly to the trickle of progress in our understanding of metazoan origins. In mammalian cells, origins are complex and heterogeneous, and appear to be selected by features of nuclear architecture that are re-established after each mitosis. Studies in Xenopus egg extracts have shown that once per cell cycle replication does not require specific origin sequences, despite the identification of functional homologues to yeast origin-binding proteins. These observations suggest that initiation of DNA replication in higher eukaryotes is focused to specific genomic regions by features of chromosome structure.