MCB Accepts, published online ahead of print on 26 October 2009

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Mol. Cell. Biol. doi:10.1128/MCB.00983-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Mss51 and Ssc1 facilitate translational regulation of cytochrome c oxidase biogenesis

Flavia Fontanesi, Iliana C. Soto, Darryl Horn, and Antoni Barrientos^*

Department of Neurology and Department of Biochemistry & Molecular Biology, University of Miami Miller School of Medicine, Miami, FL

^* To whom correspondence should be addressed. Email: abarrientos{at}med.miami.edu.

The intricate biogenesis of multimeric organellar enzymes of dual genetic origin entails several levels of regulation. In S. cerevisiae, mitochondrial cytochrome c oxidase (COX) assembly is regulated translationally. Synthesis of subunit 1 (Cox1) is contingent on the availability of its assembly partners, thereby acting as a negative feedback loop that coordinates COX1 mRNA translation with Cox1 utilization during COX assembly. The COX1 mRNA specific translational activator Mss51 plays a fundamental role in this process. Here we report that Mss51 successively interacts with the COX1 mRNA translational apparatus, newly synthesized Cox1 and other COX assembly factors during Cox1 maturation/assembly. Notably, the mitochondrial Hsp70 chaperone Ssc1 is shown to be an Mss51 partner throughout its metabolic cycle. We conclude that Ssc1, by interacting with Mss51 and Mss51-containing complexes, plays a critical role in Cox1 biogenesis, COX assembly and the translational regulation of these processes.