Nucleic Acids Research, Vol 25, Issue 2 403-409, Copyright © 1997 by Oxford University Press
C Carrillo and L Bonen
The most highly conserved structures of group II introns are the helical
domains V and VI near the 3'splice site. Within this region of each of the
four introns in the wheat mitochondrial nad7 gene encoding NADH
dehydrogenase subunit 7, there are A-C mispairs. To determine whether
C-to-U type RNA editing restores conventional A-U pairing, we sequenced
RT-PCR products from partially-spliced nad7 template RNA and
gel-fractionated, excised intron RNA. We examined transcripts from
germinating wheat embryos and seedlings because these two stages of
development show pronounced differences in steady state levels of nad7
intronic RNAs. We observed editing at only two of the six predicted sites,
and they were located at homologous positions within domain V of the third
and fourth introns. A third site was found to be edited within the
unmodelled domain VI loop of the fourth intron. Similar patterns of RNA
editing were seen in wheat embryos and seedlings. These observations, and
the presence of other non-conventional base pairs particularly within
domain V of plant mitochondrial introns, indicate weaker helical core
structure than in ribozymic group II introns. Moreover, the incompleteness
or absence of editing in wheat nad7 excised intron RNA suggests that,
although editing may contribute to splicing efficiency, it is not essential
for splicing.
ARTICLES
RNA editing status of nad7 intron domains in wheat mitochondria
Biology Department, University of Ottawa, 30 Marie Curie, Ottawa K1N 6N5, Canada.
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