Figure 10.

Model depicting Cox1p expression coupled to Shy1p-dependent cytochrome oxidase assembly. Mss51p promotes initiation and elongation of Cox1p translation (see Discussion). Cox14p and Mss51p form a ternary complex with newly synthesized Cox1p. The release of Mss51p from the ternary complex depends on a downstream Cox1p assembly step(s) perhaps involving Shy1p. According to this scheme, mutations blocking assembly trap Mss51p in the ternary complex, thereby limiting its availability for translation. In the cox14 mutant, Mss51p is still able to complex with Cox1p. The resultant binary complex is not assembly-competent causing Cox1p to be diverted to degradation with a concomitant release of Mss51p for additional rounds of Cox1p synthesis.