Journal
EMBO JOURNAL
Volume 26, Issue 15, Pages 3581-3591Publisher
WILEY
DOI: 10.1038/sj.emboj.7601802
Keywords
ATP synthase assembly; Chlamydomonas reinhardtii; chloroplast; subunit stoichiometry; translational regulation
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The (C) F1 sector from H+ -ATP synthases comprises five subunits: alpha, beta, gamma, delta and epsilon, assembled in a 3: 3: 1: 1: 1 stoichiometry. Here, we describe the molecular mechanism ensuring this unique stoichiometry, required for the functional assembly of the chloroplast enzyme. It relies on a translational feedback loop operating in two steps along the assembly pathway of CF1. In Chlamydomonas, production of the nucleus-encoded subunit gamma is required for sustained translation of the chloroplast-encoded subunit beta, which in turn stimulates the expression of the chloroplast-encoded subunit alpha. Translational downregulation of subunits beta or alpha, when not assembled, is born by the 5'UTRs of their own mRNAs, pointing to a regulation of translation initiation. We show that subunit gamma, by assembling with alpha(3)beta(3) hexamers, releases a negative feedback exerted by alpha/beta assembly intermediates on translation of subunit beta. Moreover, translation of subunit alpha is transactivated by subunit beta, an observation unprecedented in the biogenesis of organelle proteins.
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