A RIBONUCLEASE-ACTIVITY IS ACTIVATED BY HEPARIN OR BY DIGESTION WITH PROTEINASE-K IN MITOCHONDRIAL EXTRACTS OF LEISHMANIA-TARENTOLAE

A ribonuclease activity in a 100,000 x g supernatant of a Triton lysat e of a mitochondrial-kinetoplast fraction from Leishmania tarentolae i s activated by incubation with heparin or by predigestion of the lysat e with proteinase k or pronase. In vitro-transcribed pre-edited cytoch rome b mRNA is cleaved at several sites. With time, complete degradati on of the RNA occurs. All cleavages occurred within putative single-st randed regions of the RNA. No cleavage was observed with 9 S rRNA. The presence of a nonspecific nucleotide or nucleoside slows the rate of cleavage. The cleavage activity is inhibited by sodium dodecyl sulfate or phenol/chloroform extraction, is retained by a 10-kDa cutoff filte r, and passes through a 30-kDa filter. Micrococcal nuclease inhibits t he proteinase-induced activity but not the heparin-induced activity.