EXPLORING GENOME INTEGRITY PATHWAYS IN SACCHAROMYCES CEREVISIAE

Genomic DNA is under constant attack from both endogenous and exogenous DNA damaging agents like reactive oxygen species which include O2, H2O2, OH, reactive carbonyl species, alkylating agents such as estrogen and cholesterol metabolites, radiations (like UV, x-rays and gamma rays) and mutagenic chemicals. Moreover, threats to DNA integrity can also come from DNA metabolism such as replication, transcription and recombination. In order to survive and faithfully transmit the genetic material to the progeny, cells must detect the damage and activate repair mechanisms and, if the damage cannot be repaired, trigger the apoptotic program. All these processes, which are collectively known as DNA damage response (DDR), are coordinated by surveillance mechanisms often called DNA damage checkpoint, which temporarily halt or slow down cell cycle progression to provide enough time for DNA repair. The failure of the DNA damage response and other mechanisms deputed to the maintenance of genome integrity leads to a condition called “Genome Instability”, consisting in the accumulation of damage, genomic aberrations, such as mutations, gross chromosomal rearrangements and chromosome loss. Genome instability is a hallmark of cancer and a driving force in tumorigenesis. We exploit budding yeast Saccharomyces cerevisiae as a model system for studies on genome maintenance pathways which are highly conserved throughout evolution from yeast to human. Despite recent advances in the field, genome integrity pathways are not yet fully understood and not all the genes involved have been identified. We developed a screening strategy, based on the overexpression of DDC2, a critical DNA damage checkpoint gene in the contest of a yeast deletion collection, in order to identify genes controlling genome integrity on the basis of spontaneous accumulation of endogenous DNA damage. We identified several genes and pathways associated with genome integrity maintenance, among which are many genes induced in peroxisome biogenesis and mitochondria structure and function, as well as several uncharacterized ORFs.