The mitochondrial RNA ligase from Leishmania tarentolae can join RNA molecules bridged by a complementary RNA

A biochemical characterization was performed with a partially purified RNA ligase from isolated mitochondria of Leishmania tarentolae. This ligase has a K-m of 25 +/- 0.75 nM and a V-max of 1.0 x 10(-4) + 2.4 x 10(-4) nmol/mi n when ligating a nicked double-stranded RNA substrate. Ligation was negati vely affected by a gap between the donor and acceptor nucleotides. The cata lytic efficiency of the circularization of a single-stranded substrate was B-fold less than that of the ligation of a nicked substrate. These properti es of the mitochondrial RNA ligase are consistent with an expected in vivo role in the process of uridine insertion/deletion RNA editing, in which the mRNA cleavage fragments are bridged by a cognate guide RNA.