Respiratory-deficient mutants affecting various steps in the biogenesis of the respiratory complexes were transformed with three different high-copy plasmids: (1) the empty control vector, (2) the plasmid carrying the corresponding wild type gene (OXA1 for lines 1 and 2; BCS1 for lines 2 and 3; MTF2 for line 5 and RMD9 for line 6), (3) the plasmid carrying the wild type USB1 gene. The transformants were selected on minimal glucose medium lacking uracil to select for the plasmids and their growth were tested on non fermentable medium containing 2% glycerol and 2% ethanol at 28 or 36°C. +: respiratory growth; - no growth. See also Figure 4A. The oxa1 mutant carries a double amino-acid substitution E65G-F229S in the Oxa1 protein . The bcs1 mutant carries a single amino-acid substitution F342C in Bcs1p . The other mutants carry gene deletions as indicated [38, 44, 53].