Figure 1

The principle of methods used to map replication origins. (a) The location of pre-replicative complexes can be detected by purifying DNA cross-linked to ORC/MCM proteins, followed by hybridization to a microarray (represented by gray squares). Positive hybridization (black squares) indicates the location of potential origins. (b) Hybridization of early-replicating DNA (see text for details) to a microarray allows the identification of sequences that replicate before flanking DNA, and these earliest-replicating sequences must include replication origins (black/dark gray squares).