FIGURE 1.

Scheme depicting the present understanding of early CcO assembly intermediates formed during Cox1 maturation. Following translation and protein-assisted insertion into the mitochondrial inner membrane, newly synthesized Cox1 is associated with Ssc1, Mss51, Cox14, and Coa3 assembly factors, forming an assembly intermediate that can be identified by the presence of these constituents, particularly the characteristic presence of Mss51. The next assembly intermediate is characterized by the addition of the Coa1 assembly factor and the loss of Mss51 and Ssc1 (which form a distinct binary complex). Subsequently, an intermediate containing the assembly factor Shy1 is formed, which receives cofactors in a process dependent upon Cox11, Cox10, and Cox15 and begins to associate with nucleus-encoded CcO subunits, such as Cox5a and Cox6. IMS, intermembrane space.