FIGURE 4: Identification of Cox1 I¹⁰¹F as the cox23Δ suppressor.

(A) Cox1 ORF cDNA was isolated by RT-PCR. Sanger sequencing led to the identification of an A → T mutation causing an Ile to Phe substitution in Cox1 at position 101 that curiously is wild-type in S. pombe (which lacks COX23 in its genome).

(B) Probable location of the Cox1 mutation in the inner mitochondrial membrane based on sequence alignment to the Bos taurus crystal structure (1OCC.pdb).

(C) Drop test on YPD and YPGL of Cox1 WT or I¹⁰¹F-bearing haploid cells with or without introduced cox23 deletion (rows 1-4) compared to the cox23Δ spore known to contain Cox1 I¹⁰¹F (bottom, row 5).