Unwinding DNA replication

Scientists have sorted out another piece of the DNA replication puzzle by showing what might happen to histones through the process of unwinding DNA. The linkurl:findings,;http://www.sciencemag.org published in today's (December 20) __Science__, identify a complex that can shuttle histones from parent to daughter strands of DNA as it replicates. As the replication fork moves along a strand of DNA, the linkurl:nucleosomes;http://www.the-scientist.com/article/display/23392 - the 4-histone pair c

By | December 20, 2007

Scientists have sorted out another piece of the DNA replication puzzle by showing what might happen to histones through the process of unwinding DNA. The linkurl:findings,;http://www.sciencemag.org published in today's (December 20) __Science__, identify a complex that can shuttle histones from parent to daughter strands of DNA as it replicates. As the replication fork moves along a strand of DNA, the linkurl:nucleosomes;http://www.the-scientist.com/article/display/23392 - the 4-histone pair complexes around which DNA spools - must come unhinged from DNA and reassemble on each of the daughter strands following replication. Scientists knew parent linkurl:histones,;http://www.the-scientist.com/article/display/23393 in addition to newly synthesized histones, end up on the daughter strands, but they didn't know how they got there. "This gives us a first handle to gain insights into the transfer mechanism underlying the transmission of parental histones," linkurl:Genevieve Almouzni;http://www.curie.fr/recherche/themes/detail_equipe.cfm/lang/_gb/id_equipe/4.htm at the Institut Curie in Paris and an author on the paper wrote in an Email to __The Scientist__. linkurl:Jessica Tyler;http://www.uchsc.edu/molbio/tylerj.htm at the University of Colorado Health Sciences Center had shown several years ago that the histone chaperone linkurl:Asf1 can donate histones;http://www.nature.com/nature/journal/v402/n6761/abs/402555a0.html to newly replicated DNA. In this latest study, Almouzni and her colleagues showed that Asf1 not only donates histones, but also accepts histones from the parent strand of DNA. Almouzni's group, in collaboration with a team at the Danish Cancer Society in Copenhagen, isolated complexes that include Asf1, a histone dimer, and the helicase, Mcm. Asf1's association with Mcm places it at the replication fork. The evidence "for Asf1 accepting histones at the replication fork was really interesting to me, as no factor involved in chromatin disassembly at the DNA replication fork has been proposed to date to my knowledge," Tyler, who was not involved in the study, wrote in an Email to __The Scientist__. Asf1 can only bind histone dimers, noted linkurl:Anthony Annunziato;http://www.bc.edu/schools/cas/biology/facadmin/annunziato.html at Boston College, who also was not involved in the study. With that in mind, Almouzni's findings support a linkurl:model;http://www.the-scientist.com/article/display/25250 in which the histone tetramer splits into dimers at the replication fork. "The question is, linkurl:how do you assemble;http://www.jbc.org/cgi/content/full/280/13/12065 a new nucleosome," Annunziato told __The Scientist__. Is it with two dimers that are either both parental or both new, or is it one parent dimer and one new dimer? Almouzni's model doesn't "rule out or rule in either model of reassociation," Annunziato said. Almouzni wrote that she'd be interested in seeing the findings replicated in systems other than the cell line she used, and tracing the histone shuttling process biochemically. "We have put forward a simplistic model and many more components are likely to be involved..." she added.
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