Mitochondrial and chloroplast phage-type RNA polymerases
in higher plants
Hedtke, B., Börner, T., Weihe, A.
Humboldt University Berlin, Institute of Biology, Chausseestr. 117, D-10115 Berlin, Germany
In addition to the three RNA polymerases (RNAPs) transcribing the
nuclear genes, eukaryotic cells require RNAPs to express the
genes of the mitochondrial genome and, in plants, of the plastid
genome. We have characterized two nuclear genes in the higher
plant Arabidopsis thaliana displaying strong
homology to the mitochondrial RNAP from yeast which is most
similar to RNA polymerases of the single-subunit-type known from
bacteriophages (T3, T7 and SP6). The putative transit peptides of
the two polymerases were shown to be capable of targeting fusion
proteins to mitochondria and chloroplasts, respectively,
in vitro. Recently, the cDNA of a third phage-type
RNAP has been cloned and sequenced. Computational analysis of the
N terminus suggests that it is also imported into organelles.
In vitro import experiments have been initiated.
cDNAs encoding phage-type RNAPs have also been cloned from
Chenopodium album, Nicotiana tabacum, Hordeum vulgare, and
Oryza sativa.
We conclude that the mitochondrial RNAP in plants is, as in
fungi, represented by a bacteriophage-type enzyme, and that gene
duplication events have given rise to additional polymerases, at
least one of which transcribes in Arabidopsis the plastid genome
in addition to the plastid-encoded eubacteria-like RNAP. This
data is the first direct evidence for the existence of a nuclear-
encoded plastid RNA polymerase. Data will be presented on
expression of the phage-type organellar RNAPs from Arabidopsis in
E. coli. The biochemical characterization of the
recombinant enzymes is in progress.
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Thursday, April 9 |
05:10 pm |