Figure 4. The C-terminal region of Atg43 that contains a predicted transmembrane domain is required for mitochondrial localization.

(A) Schematic representation of C-terminal deleted forms of Atg43. The region conserved among fungi is highlighted in blue. The N-terminal AIM and predicted C-terminal transmembrane domain (TM) are indicated. (B) Cells expressing wild-type and C-terminal deleted forms of Atg43 from the native gene locus were collected at the indicated time points after shifting to nitrogen starvation medium and were subjected to immunoblotting. Each strain contained an integration vector expressing the mitophagy-defective form of Atg43, that lacks the 164 N-terminal aa, to maintain a normal growth rate. (C) The indicated strains were grown in EMM, and their serial dilutions were spotted onto solid YES medium for a growth assay. (D) Cells expressing wild-type and C-terminal truncated forms of GFP-tagged Atg43 were grown in EMM for microscopy. Tuf1-mRFP was detected as a mitochondrial marker. (E) Wild-type (fis1⁺) and GBP-fis1 cells co-expressing GFP-tagged Atg43 with a 60 aa deletion in the C-terminus and Tuf1-mRFP were grown in EMM for microscopy. (F) Wild-type (fis1⁺) and GBP-fis1 cells expressing full-length (wild-type) or C-terminal truncated Atg43 (Atg40ΔC60) with or without GFP fusion were collected at the indicated time points after shifting to nitrogen starvation medium. Cells were then used for immunoblotting. (G) Cells expressing the GFP-fused aa 185–224 of Atg43 and Tuf1-mRFP were grown in EMM for microscopy. A magnified view of the indicated area is shown in the right panel. (H) Mitophagy-defective atg43-1 cells with GBP-fused Fis1 were transformed to express GFP, GFP-fused aa 21–40 of Atg43, or GFP-fused Atg8. The indicated strains were collected at the indicated time points after shifting to nitrogen starvation medium and used for immunoblotting. Histone H3 was used as a loading control (LC) for immunoblotting. Scale bars represent 5 µm. BF, bright-field image.