A member of a novel Arabidopsis thaliana gene family of candidate Mg2+ ion transporters complements a yeast mitochondrial group II intron‐splicing mutant
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Titel:
A member of a novel Arabidopsis thaliana gene family of candidate Mg2+ ion transporters complements a yeast mitochondrial group II intron‐splicing mutant
Beschreibung:
<jats:title>Summary</jats:title><jats:p>Autocatalytic activity of some group II introns has been demonstrated <jats:italic>in vitro</jats:italic>, but helper functions such as the yeast MRS2 protein are essential for splicing <jats:italic>in vivo</jats:italic>. In our search for such helper factors in plants, we pursued the cloning of two <jats:italic>Arabidopsis thaliana</jats:italic> homologues, <jats:italic>atmrs2‐1</jats:italic> and <jats:italic>atmrs2‐2</jats:italic>. <jats:italic>Atmrs2‐1</jats:italic>, but not <jats:italic>atmrs2‐2</jats:italic>, complements the yeast deletion mutant of <jats:italic>mrs2</jats:italic>, and this is congruent with the prediction of two adjacent transmembrane stretches in AtMRS2‐1 and yeast MRS2 but not in AtMRS2‐2. This complementation depends on fusion of the native yeast mitochondrial import sequence to <jats:italic>atmrs2‐1</jats:italic>. A differing, non‐mitochondrial, cellular targeting in <jats:italic>Arabidopsis</jats:italic> is supported by the analysis of green fluorescent protein fusion constructs after transient transformation into plant protoplasts. Further members of what now appears to be a family of 10 <jats:italic>mrs2</jats:italic> homologues are identified in the <jats:italic>Arabidopsis</jats:italic> genome. Similarity searches with the <jats:sc>psi</jats:sc>‐<jats:sc>blast</jats:sc> algorithm in the protein database fail to identify homologues of this novel gene family in any eukaryotes other than yeasts, but do identify its distant relatedness to the <jats:italic>corA</jats:italic> group of bacterial magnesium transporters. In line with this observation, intramitochondrial magnesium concentrations are indeed restored to wild‐type levels in the yeast mutant on complementation with <jats:italic>atmrs2‐1</jats:italic>.</jats:p>