FIGURE 4.

Processed tRNAs are preferentially labeled with [α³²P]GTP in isolated mitochondria. Isolated mitochondria were incubated in transcription buffer (lanes 2,3), the optimal buffer for the A. castellanii 5′ editing activity (lanes 4,5), or a modified version of the A. castellanii buffer (lanes 6,7), in the presence of [α-³²P]GTP (lanes 2,4,6) or [α-³²P]UTP (lanes 3,5,7) as described in Materials and Methods. Lane 8 shows the position of mature tRNAs labeled with [α-³²P]ATP by the CCA-adding activity present in S100 extracts derived from Physarum mitochondria. End-labeled, denatured DNA size markers are shown in lane 1.