Intertwined translational regulations set uneven stoichiometry of chloroplast ATP synthase subunits.
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.
UMR 7141 CNRS/UPMC, Institut de Biologie Physico-Chimique, Paris, France.
Dominique
D
Drapier
Blandine
B
Rimbault
Olivier
O
Vallon
Francis-André
FA
Wollman
Yves
Y
Choquet
D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000201:enzymology; D002736:Chloroplasts / Q000201:enzymology*; D015536:Down-Regulation; D014176:Protein Biosynthesis; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*
D006180:Proton-Translocating ATPases