DNA replication timing is deterministic at the level of chromosomal domains but stochastic at the level of replicons in Xenopus egg extracts

Replication origins in Xenopus egg extracts are located at apparently random sequences but are activated in clusters that fire at different times during S phase under the control of ATR/ATM kinases. We investigated whether chromosomal domains and single sequences replicate at distinct times during S...

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Bibliographic Details
Published in:Nucleic acids research 2008-10, Vol.36 (17), p.5623-5634
Main Authors: Labit, Hélène, Perewoska, Irène, Germe, Thomas, Hyrien, Olivier, Marheineke, Kathrin
Format: Article
Language:English
Subjects:
Animals
Biochemistry, Molecular Biology
Cell Extracts
Cell Nucleus - metabolism
Chromosomes - chemistry
Chromosomes - metabolism
DNA Replication
DNA, Ribosomal - biosynthesis
DNA, Ribosomal - chemistry
Genome Integrity, Repair and
Kinetics
Life Sciences
Male
Ovum - metabolism
Replication Origin
Replicon
S Phase - genetics
Spermatozoa - metabolism
Stochastic Processes
Xenopus
Xenopus laevis
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Summary:Replication origins in Xenopus egg extracts are located at apparently random sequences but are activated in clusters that fire at different times during S phase under the control of ATR/ATM kinases. We investigated whether chromosomal domains and single sequences replicate at distinct times during S phase in egg extracts. Replication foci were found to progressively appear during early S phase and foci labelled early in one S phase colocalized with those labelled early in the next S phase. However, the distribution of these two early labels did not coincide between single origins or origin clusters on single DNA fibres. The 4 Mb Xenopus rDNA repeat domain was found to replicate later than the rest of the genome and to have a more nuclease-resistant chromatin structure. Replication initiated more frequently in the transcription unit than in the intergenic spacer. These results suggest for the first time that in this embryonic system, where transcription does not occur, replication timing is deterministic at the scale of large chromatin domains (1-5 Mb) but stochastic at the scale of replicons (10 kb) and replicon clusters (50-100 kb).
ISSN:0305-1048
1362-4962
DOI:10.1093/nar/gkn533