Deregulated replication licensing causes DNA fragmentation consistent with head-to-tail fork collision.
Correct regulation of the replication licensing system ensures that no DNA is rereplicated in a single cell cycle. When the licensing protein Cdt1 is overexpressed in G2 phase of the cell cycle, replication origins are relicensed and the DNA is rereplicated. At the same time, checkpoint pathways are activated that block further cell cycle progression. We have studied the consequence of deregulating the licensing system by adding recombinant Cdt1 to Xenopus egg extracts. We show that Cdt1 induces checkpoint activation and the appearance of small fragments of double-stranded DNA. DNA fragmentation and strong checkpoint activation are dependent on uncontrolled rereplication and do not occur after a single coordinated round of rereplication. The DNA fragments are composed exclusively of rereplicated DNA. The unusual characteristics of these fragments suggest that they result from head-to-tail collision (rear ending) of replication forks chasing one another along the same DNA template.
Davidson
Iain F
IF
School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.
Li
Anatoliy
A
Blow
J Julian
JJ
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D053938:DNA Fragmentation; D004261:DNA Replication / Q000235:genetics*; D064248:Geminin; D006801:Humans; D008957:Models, Genetic; D010063:Ovum / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013698:Templates, Genetic; D014981:Xenopus / Q000378:metabolism*; D029867:Xenopus Proteins
D018797:Cell Cycle Proteins; C577998:GMNN protein, Xenopus; D064248:Geminin; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D004247:DNA