Most mitochondrial genes of Trypanosoma brucei
do not contain the necessary information to make translatable
mRNAs. These transcripts must undergo RNA editing, a posttranscriptional
process by which uridine residues are added and deleted
from mitochondrial mRNAs. RNA editing is believed to be
catalyzed by a ribonucleoprotein complex containing endonucleolytic,
terminal uridylyl transferase (TUTase), 3′ uridine-specific
exonucleolytic (U-exo), and ligase activities. None of
the catalytic enzymes for RNA editing have been identified.
Here we describe the identification of two candidate RNA
ligases (48 and 52 kDa) that are core catalytic components
of the T. brucei ribonucleoprotein editing complex.
Both enzymes share homology to the covalent nucleotidyl
transferase superfamily and contain five key signature
motifs, including the active site KXXG. In this report,
we present data on the proposed 48 kDa RNA editing ligase.
We have prepared polyclonal antibodies against recombinant
48 kDa ligase that specifically recognize the trypanosome
enzyme. When expressed in trypanosomes as an epitope-tagged
fusion protein, the recombinant ligase localizes to the
mitochondrion, associates with RNA editing complexes, and
adenylates with ATP. These findings provide strong support
for the enzymatic cascade model for kinetoplastid RNA editing.