Tonje Tvegård, a research fellow in Erik Boye’s group, has for several years worked to understand the mechanisms regulating the start-up of DNA replication. Now she and the group has, in collaboration with Stephen Kearsey at the University of Oxford, identified and partly characterised a novel and exciting mechanism that negatively regulates S phase entry in fission yeast.
This work was recently published in the prestigiuos journal "Genes and Development" (impact factor = 15,61).
Genes & Development has been named by ISI as one of the Top 10 Hottest Journals of the Millennium (1995-2005) in the field of Molecular Biology and Genetics and one of the Highest Impact Journals in All Fields (1995-2005).
Summary of the findings (written by the authors)
It is well known that the cell cycle is stopped when the DNA is damaged by mechanisms called checkpoints. Tvegård et al show that when fission yeast cells are exposed to ultraviolet light they delay entry into the cell cycle, as predicted. Surprisingly, the mechanism of inhibition does not depend on classical checkpoint proteins, but rather to a protein kinase, called Gcn2, that is normally regulating the growth rate (protein synthesis). Therefore, the findings suggest a possible link between general cell growth and progression through the cell cycle. Another surprise was that the novel checkpoint is not induced by other DNA-damaging agents such as ionizing radiation.
Before DNA replication can occur, a pre-repicative complex (pre-RC) must be formed. This involves the loading of proteins called Mcms onto chromatin. We have used GFP-tagged Mcm6 to investigate the kinetics of pre-RC formation in synchronised fission yeast cells after UV-irradiation. In this assay, unbound GFP-MCM6 can be extracted from the cells whereas bound protein remains in the nucleus.
|A: Phase contrast image of cells where the nuclei are visualized by DAPI staining (blue).||B: Fluorescence micrograph of the same cells, showing a mixture of GFP- positive and -negative cells after extraction.|
Tvegard T, Soltani H, Skjolberg HC, Krohn M, Nilssen EA, Kearsey SE, Grallert B, Boye E.
A novel checkpoint mechanism regulating the G1/S transition. (link to abstract from PubMed)
Genes Dev. 2007 Mar 15;21(6):649-54.
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Erik Boye's group - Yeast Cell Biology (radium.no/boye)
Department of Cell Biology
Institute for Cancer Research