The N-terminal 22-amino acid region of NDUFV2 is essential and efficient for mitochondrial targeting. (a) The diagrammatic representation of EGFP fusion proteins carrying an NDUFV2 N-terminal peptide of a different length. A series of chimeric cDNA were constructed for expression of fusion proteins containing the full-length (NDUFV21-249 -EGFP), N-terminal (NDUFV21-32 -EGFP, NDUFV21-22 -EGFP, NDUFV21-21 -EGFP, NDUFV21-20 -EGFP, NDUFV21-18 -EGFP) or internal fragment (NDUFV28-22 -EGFP) in the MTS of NDUFV2 with EGFP at the C-terminus or at the N-terminus (EGFP-NDUFV21-22). The number of (+) symbols indicates the relative number of cells that exhibited EGFP fluorescence within the mitochondrial compartment in (b). The number of (+) symbols indicates that the proportion of cells exhibiting EGFP fluorescence have a typical punctuated staining pattern and mitochondrial colocalization in (b). The (++++) symbol indicates all of the EGFP fluorescence signals in transfected cells are fully colocalized with mitochondria. The (-) symbol indicates there is no cell producing EGFP fluorescence within the mitochondrial compartment. (b) The distribution of EGFP fusion proteins in transfected T-REx-293 cells was detected by EGFP fluorescence and mitochondria were labeled by Mito Tracker Red (red color). Only merged images are shown (colocalization of expressed protein and mitochondria is indicated by yellow signals). Photos A-I are corresponding to constructs A-I shown in (a). Scale bars = 10 μ m.