FIGURE 4.6 Cell cycle and regulation of DNA replication. (Courtesy of Bruce Stillman, Cold Spring Harbor Laboratory.)

noted that, because Bell and Stillman have already succeeded in getting pure preparations of the origin recognition complex (ORC), "We won't have long to wait until the individual polypeptides are purified and their genes cloned." Then, Huberman adds, "It will … be possible to compare the predicted amino acid sequences of the ORC polypeptides to those of known proteins; any similarities that turn up will suggest roles for the individual polypeptides in the initiation process." And, add Li and Alberts, "The discovery of homologues to the ORC, and analysis of their DNA binding sites, could provide a shortcut to defining replication origins in [other] higher eukaryotes."

Finally, identification of the yeast ORC may permit a scheme for replicating eukaryotic DNA in the test tube, a procedure that would



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