An RNA helicase (AtSUV3) is present in Arabidopsis thaliana mitochondria

The proteins involved in mitochondrial mRNA processing and degradation in higher plants have yet to be identified. As a first step towards this aim, we report here the characterisation of a nuclear-encoded DExH box RNA helicase (AtSUV3) localised in Arabidopsis thaliana mitochondria. The AtSUV3 mRNA is assembled from the 16 exons of a weakly expressed unique gene and the predicted protein has a calculated molecular weight of 63.6 kDa. Subcellular fractionation of transgenic plants expressing AtSUV3/GUS fusion proteins localises this protein in mitochondria. The N-terminal domain of AtSUV3 containing the motifs characteristic of DExH box RNA helicases exhibits a low endogenous ATPase activity in vitro which can be stimulated by the presence of mitochondrial RNA, confirming that AtSUV3 is an RNA helicase.