FIGURE 1.

Schematic of mt-tRNA editing in D. discoideum. 5′-Editing of mt-tRNA occurs in at least two steps in which 5′-mismatched nucleotides are removed from the 5′-end of the mt-tRNA, producing a presumed 5′-truncated mt-tRNA intermediate. Biochemical data suggest that the 5′-truncated mt-tRNA is then acted on by one of the TLP enzymes encoded by the D. discoideum nuclear genome, thus repairing the 5′-truncated end via 3′–5′ polymerase activity using the 3′-side of the aminoacyl-acceptor stem as the template for polymerase activity. The presence of an intact 3′-CCA end on the tRNA prior to editing is shown for clarity (and is supported by the sequences obtained in this work), but the precise order of 3′-processing and 5′-editing events has not been determined.