Import of small truncated RNAs into mitochondria.

(A) In vivo import of the truncated HF (left panel) and HD (middle panel) RNAs in mitochondria of the control cells and the cells overexpressing preKARS2. (B) In vivo import of HF and HD RNAs in the control cells and the cells with downregulation of preKARS2. Hybridization probes are indicated on the right of the panels. Overexpression and downregulation of preKARS2 were confirmed by Western blot as in Fig. 4A, C. The relative import efficiencies are shown on the right panels, ±SD calculated from three independent experiments. (C) Secondary structure (on the left) of the artificial control RNA, predicted by Mfold. The control RNA in vitro (middle panel, indications are as in Fig. 3) and in vivo (right panel) import tests. (D) OD280 absorption profile of HepG2 proteins separated by gel filtration on a Sephacryl G-200 column. (E) Import of HF RNA (upper panel) and HD RNA (lower panel) into isolated HepG2 mitochondria in the presence of proteins from the gel filtration fractions indicated above the lanes. Input, 2–5% of RNA used for each assay. The RNA import efficiencies calculated by comparing with the inputs, in fmoles of imported RNA per 0.1 mg of mitochondrial protein, are given below each lane. On each panel, a representative of at least three independent experiments is shown, ±SD indicated.