In Podospora anserina we have described the purification of an endo-exonuclease (Biochim. Biophys. Acta 1574 (1) (2002) 72). Given the description of several nucleases addressed to the mitochondria and known to interact with the PCNA, we sought a possible effect of PCNA on the mt nuclease. A significant stimulation of the nuclease activity with PCNA was observed with double-stranded and flap structure DNA. Immuno-Western blotting experiments realized with monoclonal antibodies raised against the PCNA specifically revealed the presence of a single band of 30 kDa in the mitochondria from the filamentous fungus and yeast. A potential PCNA binding motif was found in the sequences of several mt nucleases and mt proteins involved in the maintenance of the mt DNA with respect to the consensus described by Warbrick. The hypothetical role of the PCNA as a potential regulator of the repair/recombination processes in the maintenance of the mt genome is discussed.