摘要All members of the YidC/Oxa1/Alb3 protein family are evolutionarily conserved and appear to function in membrane protein integration and protein complex stabilization. Here, we report on a second thylakoidal isoform of Alb3, named AIM. Analysis of Arabidopsis knockout mutant lines shows that Alb4 is required in assembly and/or stability of the CF_1CF_0-ATP synthase (ATPase). alb4 mutant lines not only have reduced steady-state levels of ATPase subunits, but also their assembly into high-molecular-mass complexes is altered, leading to a reduction of ATP synthesis in the mutants.Moreover, we show that Alb4 but not Alb3 physically interacts with the subunits CF_1β and CF_0Ⅱ. Summarizing, the data indicate that Alb4 functions to stabilize or promote assembly of CF_1 during its attachment to the membrane-embedded CF_0 part.