Required for alpha-carboxysome (Cb) assembly, mediates interaction between RuBisCO and the carboxysome shell. The protein is probably intrinsically disordered. The C-terminal repeats act as the encapsulation signal to target proteins to the Cb; they are necessary and sufficient to target both CsoS2 and foreign proteins to the Cb. The N-terminal repeats of this protein bind simultaneously to both subunits of RuBisCO. Probably also interacts with the major shell proteins (CsoS1); that interaction would increase the local concentration of CsoS2 so that it can condense RuBisCO and full carboxysomes can be formed. Interacts via its N-terminal repeats with RuBisCO. Interacts with the major shell protein CsoS1. Down-regulated with rising temperature (from 25 to 28 degrees Celsius) in both nitrate- and urea-grown cells (at protein level). Has 3 domains; the N-terminal domain has 4 short repeats and binds RuBisCO. The central region has 6 longer repeats. The C-terminal domain has 2 repeats and a highly conserved C-terminal peptide. The C-repeats serve as the encapsulation signal for the alpha-carboxysome, and are able to target foreign proteins to this organelle. Unlike H.neapolitanus and predictions for P.marinus strain MIT 9313, this protein is not thought to have ribosomal frameshifting. Belongs to the CsoS2 family.