Dynamics of the Genome - CNRS URA2171  

  HEADArcangioli Benoit, Dr / barcan@pasteur.fr
  MEMBERSBenhassine Samia / Dr Holmes Allyson / Roseaulin Laura / Schurra Catherine / Lavenir Armelle

  Annual Report

We identified the cis-acting elements responsible for the imprint at the mating-type locus in the fission yeast, Schizosaccharomyces pombe. The molecular nature of the imprint has been determined as a single-strand break, and we constructed and validated an inducible mating-type switching system. We showed that Pli1 encodes for a SUMO E3-ligase, which plays an important role for centromere and telomere maintenance as well as chromosome stability.

Our previous works allowed us to show that a programmed strand-specific modified nick at the mat1 locus constitute a novel chromosomal imprinting. This DNA lesion is the initial event triggering mating-type switching in this yeast. Polar replication pausing and termination at mat1 is essential for the formation of the imprint.

Recently, we constructed and validated a powerful inducible nick and mating-type switching system. Starting with a homogenous cell population (a single mating-type and no break), we were able to study the kinetics of each cellular step. We found that the overall process of MT switching in S. pombe is a two-step process, involving two rounds of DNA replication (See Figure).

The role of recombination in the recovery of stalled/collapsed replication forks is an essential process in maintaining genomic stability and defects in this pathway cause predisposition to many forms of diseases. We show that a unique collapsed replication fork at the mating-type locus required the homologous recombination enzymes for viability in fission yeast.

SUMO is covalently conjugated to certain proteins, in a similar multistep process to ubiquitination, and seems to direct their targets to particular cellular locations/structures. In collaboration with J. Seeler (Unité de l'Organisation Nucléaire et Oncogénèse), have shown that Pli1 is an E3 SUMO-ligase in vivo and in vitro. Our genetic studies indicated that SUMO modification plays an important role in the protection of repetitive elements within heterochromatin from illegitimate homologous recombination and negatively control the telomerase activity.

Keywords: Stem cell, imprinting, replication, recombination, cancer, ataxia


Mating-type switching pattern (From Klar, 1990). P and M indicate the mating-type of the cell, the suffix u or s represents the unswitchable and switchable potential of the cell, respectively. For simplicity, only the P lineage is shown (mirror image of the M). The one-in four and the consecutive switching rules are indicated. The overall pattern is similar to stem cell division in higher eukaryotes.


Kaykov, A., Holmes, A.M., and Arcangioli, B. (2004) Formation, maintenance and consequences of the imprint at the mating-type locus in fission yeast. EMBO J. 23, 930-938.

Xhemalce, B., Seeler, J-S., Thon, G., Dejean, A., and Arcangioli, B. (2004) Role of the fission yeast SUMO E3 ligase Pli1p in centromere and telomere maintenance. EMBO J. 19 :3844-3859.

Kaykov A. and Arcangioli, B. (2004) A programmed strand-specific and modified nick in S. pombe constitutes a novel chromosomal imprint. Curr. Biol. 14 :R915-917.

Holmes A., Kaykov, A. and Arcangioli B. (2005) Molecular and Cellular Dissection of mating-type switching steps in S. pombe. Mol. Cell. Biol., :303-311.

Xhemalce B, Miller KM, Driscoll R, Masumoto H, Jackson SP, Kouzarides T, Verreault A, Arcangioli B. (2007). Regulation of histone H3 lysine 56 acetylation in Schizosaccharomyces pombe. J Biol Chem., 282 :15040-7

Activity Reports 2007 - Institut Pasteur
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