Studies on the catalytic properties of the calcium-dependent endoribonuclease of Trypanosoma brucei cytoplasm.

A calcium-dependent endoribonuclease isolated from Trypanosoma brucei cytoplasm has been further characterized. The products of exhaustive endonuclease digestion of poly(A), which the enzyme cleaved preferentially, were small oligonucleotides terminated by a 5'-phosphoryl group. Its apparent Km value was 0.8 mM using poly (A), and 3.3 mM using transfer RNA. The base specificity of the endoribonuclease was further verified by using synthetic heteropolyribonucleotides as substrates. The enzymatic reaction was inhibited by polyamines, polyanions, iodoacetic acid and the heavy metals, but only very slightly by N-ethylmaleimide and iodoacetamide. A possible implication of the enzyme in the turnover of messenger RNA is discussed.