Genetic network interactions among replication, repair and nuclear pore deficiencies in yeast

The yeast RAD27 gene encodes a functional homolog of the mammalian FEN1 protein, a structure-specific endo/exonuclease which plays an important role in DNA replication and repair. Previous genetic interaction studies, including a synthetic genetic array (SGA) analysis, showed that the survival of rad27Δ cells requires several DNA metabolic processes, in particular those mediated by all members of the Rad52-dependent recombinational repair pathway. Here, we report the results of our SGA analysis of the collection of non-essential yeast genes against the rad27Δ mutation, which resulted in the identification of a novel synthetic lethal interaction conferred by mutations affecting the Nup84 nuclear pore subcomplex (nup133Δ, nup120Δ and nup84Δ). Additional screens showed that all Rad52 group genes are required for the survival of the nup133Δ and nup120Δ mutants, which are defective in nuclear pore distribution and mRNA export, but not of the nup133ΔN mutant, which is solely defective in pore distribution. This requirement for the DNA double-strand break (DSB) repair pathway is consistent with the observation that, like rad27Δ, the nup133Δ, nup120Δ and nup84Δ mutants are sensitive to methyl methanesulfonate (MMS). Furthermore, nup133Δ cells exhibit an increased number of spontaneous DNA repair foci containing Rad52. Altogether, these data suggest that the pathological interactions between the rad27Δ and specific nupΔ mutations result from the accumulation of unrepaired DNA damages.