The open reading frame 1-encoded protein (36K) of carnation Italian ringspot virus localized to mitochondria.

The localization of the 36 kDa (36K) protein encoded by the open reading frame (ORF) 1 of Carnation Italian ringspot virus was studied in infected cells and in cells transiently expressing this protein fused to the green fluorescent protein (GFP). Subcellular fractionation demonstrated that the 36K protein accumulated in fractions containing mostly mitochondria. Fluorescence microscopy of transiently transformed cells showed that the 36K-GFP fusion protein accumulated in structures which could be stained with the mitochondrial specific dye MitoTrackerTM. However, these structures were larger than normal mitochondria and irregular in shape and distribution in the cytoplasm. Electron microscopy showed severe alterations of mitochondria which were often clumped. The stroma was more electron-opaque, the cristae were irregularly shaped, the intermembrane space was enlarged and the outer membrane was covered by an electron-dense amorphous material whose nature could not be determined. The organelle-targeted 36K seems to promote overgrowth of the mitochondrial outer membrane.