Simultaneous isolation of cytoplasmic endoribonuclease and exoribonuclease of Trypanosoma brucei

An endoribonuclease and an exoribonuclease have been isolated simultaneously from the cytoplasm of Trypanosoma brucei by hydroxyapatite column chromatography. The endoribonuclease produced oligonucleotides from poly(adenylic acid) with 5′-phosphate and 3′-OH termini. The exoribonuclease produced only ribonucleoside 5′-phosphates from poly(adenylic acid). The relative rates of degradation of synthetic homopolynucleotides by the endoribonuclease under standard conditions were in the order poly(adenylic acid) > poly(uridylic acid) {geometrically equal to} poly(cytidylic acid); for the exoribonuclease the order was poly(adenylic acid) {geometrically equal to} poly(uridylic acid) > poly(cytidylic acid). Natural transfer and ribosomal RNAs were also degraded by both enzymes, while DNA was resistant to them. The optimal pH of activity for each enzyme was 7.5-8.0. Both ribonucleases require Ca2+ for maximum enzymatic activity. © 1985.