(A) On the left and central panels is the surface representation of the hEXO-14cat cryo-EM structure. On the right is a cartoon representation of the yExo-14 structure from (Schuller et al., 2018, PDB: 6fsz), shown in the same orientation and color coding. (B) On the left is a growth assay of wild-type and mutant mtr4 strains. Endogenous MTR4 was replaced with wild-type or mutant mtr4-EGFP fusions. Cells were grown to early exponential phase, and serial dilutions were spotted onto 5-fluoroorotic acid (FOA) medium or control plate. Medium containing FOA selects for the loss of the rescue vector. SC, synthetic complete medium; YPD, yeast extract peptone adenine dextrose; FOA, 5-fluoroorotic acid. ΔSK corresponds to an arch-less mutant of yMtr4 (Falk et al., 2014) On the right is the analysis of the expression levels of wild type yMtr4-EGFP and mutants by Western blotting using an anti-GFP antibody.