In his Part 3, Rutter emphasizes the challenge of mitochondrial protein synthesis. How do the components of the electron transport chain (ETC) assemble in the right stoichiometry at the right time? Rutter introduces the LYR family of proteins, which aid assembly of ETC components. LYR proteins interact with a common binding partner, the acyl carrier protein (ACP), via a unique fatty acyl moiety on ACP. Rutter’s group showed that ACP acylation is necessary for assembly of the ETC and activation of oxidative phosphorylation.