Isolation and Characterization of a U-specific 3′5′ -Exonuclease from Mitochondria of Leishmania tarentolae

Abstract

We have purified a 3′-5′-exoribonuclease from mitochondrial extract of Leishmania tarentolae over 4000-fold through six column fractionations. This enzyme digested RNA in a distributive manner, showed a high level of specificity for 3′-terminal Us, and was blocked by a terminal dU; there was slight exonucleolytic activity on a 3′-terminal A or C but no activity on a 3′-terminal G residue. The enzyme preferred single-stranded 3′-oligo(U) overhangs and did not digest duplex RNA. Two other 3′-5′-exoribonuclease activities were also detected in the mitochondrial extract, one of which was stimulated by a 3′-phosphate and the other of which degraded RNAs with a 3′-OH to mononucleotides in a processive manner. The properties of the distributive U-specific 3′-5′-exoribonuclease suggest an involvement in the U-deletion RNA editing reaction that occurs in the mitochondrion of these cells.