Figure 4A. Size exclusion chromatography elution profile (1.6 cm × 50 cm Superdex S75) and SDS-PAGE of full-length N-terminally 7×His tagged yeast Oxr1. B. Inhibition of V1ΔH and V1Hchim's MgATPase activity by Oxr1 in absence and presence of subunit C. The data from one representative of two experiments using two different preparations are shown. Individual data points (n=2) and mean from one representative of two biological replicates are shown with error bars representing S.E.M. . C. Oxr1 binds wild type V1. Samples of V1, Oxr1, and mixtures of V1 with a 2-fold molar ratio of Oxr1 in absence or presence of a 3-fold molar ratio of subunit C were subjected to size exclusion chromatography on a 1 cm × 30 cm Superose 6 Increase column. SDS-PAGE is shown for all four samples and immunoblot analysis of column fractions using a penta-His antibody is shown for samples containing Oxr1 and Oxr1 plus C. Note that incubation of V1 with Oxr1 in presence of excess subunit C leads to partial release of subunit H (highlighted by the rectangular box in the V1 + Oxr1 + C gel). Also, some degradation of Oxr1's unstructured N-terminus is observed as indicated by the asterisk (only the full-length protein is detected by the αHis-tag antibody). The data from one representative of two experiments using two different preparations are shown. D. Dissociation kinetics of Hwt and Hchim from V1ΔH in presence of Oxr1 and subunit C as probed by BLI. Recombinant wild type (left) and chimeric subunit H (right) with an N-terminal fusion to maltose binding protein (MBP) was immobilized on anti-mouse Fc (AMC) BLI sensors via an αMBP monoclonal antibody. The sensors were then dipped into wells with V1ΔH followed by wells with buffer in absence or presence of Oxr1 and C to monitor the kinetics of V1ΔH dissociation. Only the dissociation phase is shown. The data from one representative of three experiments using two different preparations are shown. E. Oxr1 mediated inhibition of assembly of holo V-ATPase from V1Hchim, subunit C and VoND. The data from one representative of two experiments using two different preparations are shown. Individual data points (n=2) and mean from one representative of two biological replicates are shown with error bars representing S.E.M. . F. Oxr1 prevents binding of V1Hchim to VoND as probed by BLI. Streptavidin coated BLI sensors were loaded with Vo in lipid nanodiscs containing biotinylated MSP, and sensors were then dipped into wells containing recombinant C and V1Hchim in absence and presence of Oxr1. Only the V1Hchim association and dissociation phase from one representative of two experiments using two different preparations is shown. G. Oxr1 mediated dissociation of holo V-ATPase as analyzed by negative stain electron microscopy. V1HchimVoND was incubated without and with a 3-fold molar ratio of Oxr1 for 16 h. Samples were then spotted on carbon coated copper grids, stained with 1% uranyl acetate and observed by transmission electron microscopy. Number of assembled V1Vo and disassembled V1 and Vo particles were counted on a total of 20 micrographs each. The horizontal dotted lines indicate the mean. A few holoenzyme and free V1 and VoND particles are highlighted by white circles and boxes, respectively. Bar = 50 nm. The data from one representative of two experiments using two different preparations are shown.