PT  - JOURNAL ARTICLE
AU  - Walter, Johannes
AU  - Newport, John W.
TI  - Regulation of Replicon Size in <em>Xenopus</em> Egg Extracts
AID  - 10.1126/science.275.5302.993
DP  - 1997 Feb 14
TA  - Science
PG  - 993--995
VI  - 275
IP  - 5302
4099  - http://science.sciencemag.org/content/275/5302/993.short
4100  - http://science.sciencemag.org/content/275/5302/993.full
SO  - Science1997 Feb 14; 275
AB  - Once a specific number of cells have been produced in the early Xenopus laevis embryo, replicon size during the S phase of the cell cycle increases. Here, it is reported that similar increase in replicon size occurred when the concentration of nuclei in replication-competent Xenopus egg extracts exceeded a critical threshold. In this system, the origin recognition complex (ORC) did not become stoichiometrically limiting for initiation, and similar amounts of this complex bound to chromatin regardless of replicon size. These data suggest that in early development, an unidentified factor controls how many preformed ORC-DNA complexes initiate DNA replication.