Characterization of a novel NTP-dependent 3' exoribonuclease from yeast mitochondria

We have purified and characterized a novel exoribonuclease that was isolated from the mitochondria of Saccharomyces cerevisiae. The enzyme degraded RNA in a 3' to 5' direction and was dependent on nucleotide triphosphates for activity. All eight of the standard ribo- and deoxyribonucleotide triphosphates supported activity with an apparent Km ranging from 20 to 90 uM. The enzyme also exhibited an RNA-dependent ATPase activity. Evidence suggests that in vivo the enzyme may associate with mitochondrial factors which can alleviate the dependence on nucleotide triphosphates for enzymatic activity. A model is discussed for the role of the enzyme in regulating the turnover of mitochondrial RNAs.