Translation Site of the Cytochrome Oxidase Subunits

In order to define the translation site of the individual cytochrome oxidase subunits, cytochrome oxidase was purified from double-labeled cells. These had first been labeled with [ C]leucine in the absence of inhibitors, followed by labeling with [ H]leucine, either in the absence of inhibitors or in the presence of cycloheximide or chloramphenicol (see Section 2). The purified cytochrome oxidase was subsequently separated into subunits by gel electrophoresis in dodecylsulfate. The distribution of and H radioactivity was analyzed (Table I, Fig. 7). 

In untreated cells serving as control (labeling procedure 1, Section 2) no significant difference in the H/ C ratio of the seven cytochrome oxidase subunits could be detected (Fig. 7A). This indicates that these subunits 

From labeling experiments II and IV (Table I, Figs. 7B and D), the following conclusion can be drawn The three large cytochrome oxidase subunits are mitochondrial translation products their labeling is insensitive to cycloheximide, but is sensitive to chloramphenicol. The four small cytochrome oxidase subunits are cytoplasmic translation products their labeling is sensitive to cycloheximide, but is insensitive to chloramphenicol. 

---