sentence: The report also showed that PCNA strongly stimulates the 3 ′ – 5 ′ exonuclease and 3 ′ - phosphodiesterase activities of Ape2 , but has no effect on its AP-endonuclease , as the case of S. cerevisiae Ape2.We have been studying the PCNA-interacting proteins from the hyperthermophilic euryarchaeon Pyrococcus furiosus ( 23 – 27 ) .