Several mutations in MIP1, but not all, were rescued, albeit at different extent, by treatment with dihydrolipoic acid or with the mitochondrial specific ROS scavenger MitoQ. To know whether this effect could be increased by REV3 overexpression the petite frequency was measured either in haploid or in heteroallelic strains treated with these molecules. We found that there was a negative correlation between the rescue exerted by ROS scavengers and the rescue caused by REV3 overexpression. In fact, in haploid strains harboring A692T and G807R mutations, whose effect was reduced by overexpression of Rev3, no rescue was exerted by dihydrolipoic acid or MitoQ. In contrast, ROS scavengers strongly mitigated the effect of mip1 mutations E698G, K749R, Y757C, that are insensitive to Rev3 overexpression. The only exception was mutation C261R, whose effect was slightly rescued both by treatment with ROS scavengers and by Rev3 overexpression. In this case, the additive effect of Pol zeta overexpression and ROS scavengers suggested that two different mechanisms wereLY294002involved in the reduction of petite mutability observed. The second mechanism able to rescue the mip1 induced mtDNA extended mutability is the increase of the dNTP pools. In S. cerevisiae an increase of the dNTP pool was obtained either by overexpressing RNR1 gene, which encodes the large subunit of the ribonucleotide reductase or by deleting SML1 gene, which encodes an inhibitor of the latter activity. It has been shown that overexpression of RNR1 or deletion of SML1, reduced the petite frequency in strainsMasitinib inhibitor harboring specific MIP1 mutations. It was previously shown that in UV-treated cells, enhanced expression of REV3 led to increase of nuclear point mutability, measured as increase in the rate of arg4–17 reversion. Pol zeta mutagenic function is dependent on Rev1 protein. We measured nuclear mutability in cells transformed with REV3 and/ or REV1 overexpressing plasmids to determine whether increased levels of Pol zeta/Rev1 exerted mutagenic effect as a consequence of a general mechanism associated to the translesion bypass. The overexpression of Rev3 or Rev1 caused an approximately two-fold increase of nuclear point mutability, measured as rate of CanR mutants. When both Pol zeta and Rev1 were overexpressed, the rate of CanR mutations increased approximately 3-fold. Thus, overexpression of Pol zeta is useful to reduce the mtDNA instability caused by specific mutations in MIP1 but is detrimental to spontaneous nuclear mutability. To evaluate the localization of Rev3, we first cloned the whole coding sequence either in a centromeric plasmid or in a multicopy plasmid in frame with the EGFP gene.