THE PLANT CELL, Vol 5, Issue 12 1843-1852, Copyright © 1993 by American Society of Plant Biologists
RNA Editing in Plant Mitochondria: [alpha]-Phosphate Is Retained during C-to-U Conversion in mRNAs
V. K. Rajasekhar and R. M. Mulligan
Department of Developmental and Cell Biology, University of California, Irvine, California 92717
RNA editing in higher plant mitochondria frequently results in the
post-transcriptional conversion of specific cytidine residues to uridine
residues and infrequently results in the reverse conversion. The mechanisms
by which this transition could occur are deamination or transamination of
the amide at C-4 of cytosine, transglycosylation of the ribosyl residue, or
deletion of a CMP residue and insertion of a UMP residue. Intact maize or
petunia mitochondria were supplied with [alpha]-32P-CTP to radiolabel CMP
residues in the nascent transcripts, and the fate of the [alpha]-phosphate
was examined by digestion of the RNA to nucleotide monophosphates and
analysis by two-dimensional chromatography. A small fraction of
radioactivity comigrated with UMP on two different two-dimensional
thin-layer chromatography systems, and the amount of radiolabeled UMP
increased between l0-min and 2-hr incubations. The conversion of
cytidine-to-uridine residues was detected in the highly edited mRNA
fraction but was not detected in the rRNA fraction. Recovery of
radiolabeled UMP residues suggests that the [alpha]-phosphate is retained
during the editing reaction. These results are consistent with either
deamination or transamination, or transglycosylation mechanisms for RNA
editing.
