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Xenopus egg extracts treated with the protein kinase inhibitor 6-dimethylaminopurine (6-DMAP) are unable to support the initiation of DNA replication. Nuclei assembled in 6-DMAP extracts behave as though they are in G2, and will not undergo another round of DNA replication until passage through mitosis. 6-DMAP extracts are functionally devoid of a(More)
In late mitosis and early G1, replication origins are licensed for subsequent use by loading complexes of the minichromosome maintenance proteins 2-7 (Mcm2-7). The number of Mcm2-7 complexes loaded onto DNA greatly exceeds the number of replication origins used during S phase, but the function of the excess Mcm2-7 is unknown. Using Xenopus laevis egg(More)
The cyclins are a family of proteins encoded by maternal mRNA. Cyclin polypeptides accumulate during interphase and are destroyed during mitosis at about the time of entry into anaphase. We show here that Xenopus oocytes contain mRNAs encoding two cyclins that are major translation products in a cell-free extract from activated eggs. Cutting these mRNAs(More)
This paper reviews our current knowledge of the cyclins based on observations of the oocytes and eggs of sea urchins, clams and frogs. Cyclins are proteins found in all eukaryotes whose special property is rapid destruction at specific stages in the cell cycle. The cyclins fall into three families. A-type cyclins have been found in clams, flies and frogs.(More)
BACKGROUND Cip1 is a 21 kD protein that interacts with and inhibits cyclin-dependent kinases (cdks). Expression of Cip1 is induced by the tumour suppressor p53, and tumour cells have greatly reduced levels of Cip1. As cdks are required for normal progression through the cell cycle, their inhibition by Cip1 may mediate the ability of p53 to block cell(More)
Extracts of activated Xenopus eggs in which protein synthesis has been inhibited support a single round of chromosomal DNA replication. Affinity-depletion of cyclin dependent kinases (Cdks) from these extracts blocks the initiation of DNA replication. We define 'S-phase promoting factor' (SPF) as the Cdk activity required for DNA replication in these(More)
In most eukaryotes, replication origins fire asynchronously throughout S-phase according to a precise timing programme. When replication fork progression is inhibited, an intra-S-phase checkpoint is activated that blocks further origin firing and stabilizes existing replication forks to prevent them undergoing irreversible collapse. We show that chromatin(More)
Accurate DNA replication requires proper regulation of replication licensing, which entails loading MCM-2-7 onto replication origins. In this paper, we provide the first comprehensive view of replication licensing in vivo, using video microscopy of Caenorhabditis elegans embryos. As expected, MCM-2-7 loading in late M phase depended on the prereplicative(More)
Before S phase, cells license replication origins for initiation by loading them with Mcm2-7 heterohexamers. This process is dependent on Cdc6, which is recruited to unlicensed origins. Using Xenopus egg extracts we show that although each origin can load many Mcm2-7 hexamers, the affinity of Cdc6 for each origins drops once it has been licensed by loading(More)
Faithful transmission of genomic information requires tight spatiotemporal regulation of DNA replication factors. In the licensing step of DNA replication, CDT-1 is loaded onto chromatin to subsequently promote the recruitment of additional replication factors, including CDC-45 and GINS. During the elongation step, the CDC-45/GINS complex moves with the(More)