Tob38 is essential for the biogenesis of β-barrel proteins. (A) Downregulation of Tob38 affects cell growth. Wild-type cells and cells expressing Tob38 under control of the GAL10 promoter (GAL-TOB38) were shifted from galactose-containing medium to glucose-containing medium at time zero. (B) Levels of Tob38, Mas37, Tob55 and of β-barrel proteins are reduced in mitochondria from cells depleted of Tob38 for 12 h (Tob38, single arrow) or 19 h (Tob38, double arrows), as determined by immunodecoration with antibodies against the indicated proteins.