Mitochondrial translation of subunits of the rotenone-sensitive NADH:ubiquinone reductase in Neurospora crassa.

The rotenone sensitive NADH:ubiquinone was isolated from mitochondria of Neurospora crassa as a monodisperse preparation with the apparent mol. wt. in Triton solution of 0.9 X 10(6). The enzyme is composed of at least 22 subunits with apparent mol. wts. in SDS between 70 and 11 kd. Six of the subunits with the mol. wts. 70, 48, 37, 25, 22 and 18 kd were radioactively labelled in the enzyme isolated from cells which had incorporated [35S]methionine in the presence of cycloheximide. These subunits are synthesized in the mitochondria. Eleven subunits were radioactively labelled in the enzyme from cells which had incorporated [35S]methionine in the presence of chloramphenicol. These subunits are synthesized in the cytoplasm. The site of translation of the other subunits could not be established by the pulse-labelling technique. The assignment of the mitochondrially synthesized subunits to unidentified reading frames on the mitochondrial DNA is discussed.