In vitro RNA editing‐like activity in a mitochondrial extract from Leishmania tarentolae.

A mitochondrial extract from Leishmania tarentolae directs the incorporation of uridylate (U) residues within the pre‐edited domain of synthetic cytochrome b (CYb) and NADH dehydrogenase subunit 7 mRNA. This has several characteristics of an in vitro RNA editing activity, but no direct evidence for involvement of guide RNAs was obtained. Inhibition by micrococcal nuclease suggests a requirement for some type of endogenous RNA. The limitation of internal U‐incorporation to the pre‐edited region in the CYb mRNA and the inhibition by deletion or substitution of both mRNA anchor sequences for CYb gRNA‐I and ‐II could be consistent either with a gRNA‐mediated process or a secondary structure‐mediated process. A low level of incorporation of [alpha‐32P]CTP occurs at the same sites as UTP. Internal U‐incorporation activity is selectively inhibited by heterologous RNAs, suggesting an involvement of low affinity RNA‐binding proteins which can be competed by the added RNA.