E-mail : Antonio.Conconi@USherbrooke.ca
Telephone : 819 821-8000 poste 75360
Fax : 819 820-6831
Environmental agents such as the ultraviolet (UV) component of sunlight, ionizing radiation, numerous genotoxic chemicals and pollutants cause DNA damage. If not repaired, DNA damage can lead to mutations and increased risk for cancer.
On the other hand, nearly half of the drugs used in chemotherapy make DNA lesions, since DNA damage induced by these compounds block DNA transcription and replication, thereby arresting cell proliferation. Therefore, a better understanding of DNA repair in living cells is of paramount importance to health science, and is the objective of the research ongoing in my laboratory.
The genome is organized into nuclear sub-domains, which create microenvironments favoring distinct chromatin structures and functions (e.g., highly repetitive sequences, centromeres, telomeres, inactive genes, RNA polymerase II and RNA polymerase III transcribed genes, and the nucleolus). Correlations have been drawn between gene silencing and its proximity to a heterochromatic compartment. For instance, yeast telomeres are clustered at the nuclear periphery, are formed onto an altered chromatin structure that shares features with heterochromatin, and silences adjacent genes. At the other end of the scale are ribosomal genes (rDNA), which are transcribed at a very high rate by RNA polymerase I (~60% of total transcription), have a loose chromatin structure and are clustered in the nucleolus. Thus, we propose that the kinetics of DNA repair vary among the nuclear sub-domains. To better understand the mechanisms of DNA repair and how cells maintain the integrity of the genome, we analyze DNA repair in different chromosomal contexts.
There are 4 categories of DNA repair: Recombination-, Mismatch-, Base excision- and Nucleotide excision (NER)- repair. In general, these repair pathways function independently since they are rather specialized for different groups of DNA lesions. However, under certain circumstances extensive cross-talk can occur between repair pathways. In my laboratory we study NER, which is performed by a large multi-enzymatic complex and removes numerous types of lesions from the DNA, including: bulky adducts caused by chemicals, inter- or intra-strand cross-links and UV photoproducts. UV light induces two major types of damage: cyclobutane pyrimidine dimers and (6-4) photoproducts, both of which are associated with skin cancer.
NER in yeast presents most of the hallmarks of NER in human cells. The strength of the yeast system relies on both genetic and biochemical approaches, which combined make a powerful tool to study intricate processes such as DNA repair in chromatin. Currently, we study NER in RNA polymerase I, -II and -III transcribed genes (in their active and inactive chromatin states) and NER of the specialized chromatin structure at the chromosomes ends, in yeast.
Grisenbeck J, Wittner M, Charton R and Conconi A. (2012) Chromatin Endogenous cleavage and psoralen crosslinking assays to analyze rRNA gene chromatin in vivo. In: Transcriptional Regulation: Methods and Protocols. Methods Mol Biol 809, 291-301 Humana press NY
Pelloux J, Tremblay M, Wellinger RJ and Conconi A (2012) UV induced DNA damage and DNA repair in ribosomal genes chromatin. In: Transcriptional Regulation: Methods and Protocols. Methods Mol Biol 809, 303-320 Humana press NY
Toussaint M, Wellinger RJ and Conconi A (2010) Differential participation of homologous recombination and nucleotide excision repair in yeast survival to ultraviolet light radiation Mutat Res698, 52-59
Tremblay M, Toussaint M, D’Amours A and Conconi A (2009) Nucleotide excision repair and photolyase repair of UV photoproducts in nucleosomes; assessing the existence of nucleosome and non-nucleosome rDNA chromatin in vivo. Biochem Cell Biol 87, 337-346(review)
Tremblay M, Teng Y, Paquette M, Waters R and Conconi A (2008) Complementary roles of yeast Rad4p and Rad34p in nucleotide excision repair of active and inactive rRNA gene chromatin. Mol Cell Biol 28, 7504-7513
Catala M, Tremblay M, Samson E, Conconi A and Abu Elela S (2008) Deletion of Rnt1p alters the proportion of open versus closed rRNA gene repeats in yeast. Mol Cell Biol 28, 619-629
Conconi A(2007) Yeast as a model system to study DNA damage and DNA repair. In: Sourcebook of Models for Biomedical Research, pp. 445-453 (ed. P.M. Conn), Humana Press, Totowa NJ
Toussaint M and Conconi A (2006) High-throughput and sensitive assay to measure yeast cell growth: a bench protocol for testing genotoxic agents. NATURE Prot 1, 1922-1928
Toussaint M, Levasseur G, Gervais-Bird J, Wellinger RJ, Abou Elela S and Conconi A (2006) A high throughput method to measure the sensitivity of yeast cells to genotoxic agents in liquid cultures. Mutat Res 606, 92-105