Dynamics of the Genome - CNRS URA2171  

  HEADARCANGIOLI Benoit / barcan@pasteur.fr

  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 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 lesion.

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.


Profil du changement de type sexuel (Klar, 1990). P (Plus) et M (Minus) indiquent le type sexuel de la cellule et le suffixe u et s indiquent le potentiel de changement lors de la prochaine division (u: pas de changement; s: changement). Par simplicité, le lignage P est montré, celui de M étant identique. Deux divisions successives sont nécessaires pour le premier changement. Ce profil de division asymétrique est similaire à celui qui est observé chez les cellules souches des eucaryotes supérieurs.

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.


Publications 2006 of the unit on Pasteur's references database

Activity Reports 2006 - Institut Pasteur
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