THE PLANT CELL, Vol 8, Issue 1 107-117, Copyright © 1996 by American Society of Plant Biologists
Incomplete Editing of rps12 Transcripts Results in the Synthesis of Polymorphic Polypeptides in Plant Mitochondria
C. G. Phreaner, M. A. Williams and R. M. Mulligan
Department of Developmental and Cell Biology, University of California-Irvine, Irvine, California 92717
C-to-U editing causes specific nucleotide changes in plant mitochondrial
mRNAs that are required for the restoration of the evolutionarily conserved
amino acid sequence. Transcripts for the ribosomal protein S12 gene (rps12)
have six C-to-U editing sites and are highly heterogeneous as a result of
incomplete editing. Immunological analysis demonstrated that unedited or
partially edited transcripts as well as edited mRNAs are translated. The
edited rps12 translation products accumulate as ribosomal subunits, but the
unedited rps12 translation products are present as unassembled subunits and
are not detected in the ribosomes. Thus, gene expression is polymorphic as
a result of incomplete C-to-U editing, and aberrant polypeptides are
present from the translation of these mRNAs. However, because only the
edited translation products accumulate in mitochondrial ribosomes, the
overall expression of rps12 is rendered coherent by the selection of edited
translation products for ribosomal biogenesis.
