The Bacterial Carbon-Fixing Organelle Is Formed by Shell Envelopment of Preassembled Cargo
(A) RuBisCO seeds assemble from protomers over time. (B) Late in the assembly process, shell proteins rapidly assemble around RuBisCO. (C) Shell closure completes the carboxysome to establish an oxidizing environment, sealing RuBisCO from the cytosol. (D) A new RuBisCO nucleus forms after completion of the previous carboxysome. Colocalization may be driven by bisection of excess cargo by shell closure, or (E) by affinity of RuBisCO assemblies initiated elsewhere to the outside of the shell. (F) Rupture of a complete carboxysome would expose old RuBisCO cargo to template new assembly.