Separation, amino-terminal sequence and cell-free synthesis of the smallest subunit of sweet potato cytochrome c oxidase.

The smallest subunit (V) of sweet potato cytochrome c oxidase was separated into three polypeptides, Va, Vb and Vc with different molecular masses (7.4 kDa, 6.8 kDa and 6.2 kDa respectively) by highly resolving sodium dodecylsulfate polyacrylamide gel electrophoresis. Antibody against subunit V reacted specifically with the polypeptide Vc. When polyadenylated mRNA from sweet potato root tissue was translated in a wheat germ cell-free system, the smallest subunit (Vc) of the polypeptides was synthesized to the same size as the mature form, which suggests that the mature subunit retains the signal for import into mitochondria. Within the N-terminal first 25 amino acids there is a stretch of 16 non-polar residues, periodically linked by basic residues, which might form an amphiphilic helix as the targeting signal.