Required for carboxysome formation; the N-terminus interacts with CcmM which itself binds RuBisCO (ribulose bisphosphate carboxylase, rbcL-rbcS) (PubMed:17993516). May also contact shell protein CcmK to help assemble the carboxysome (By similarity). Beta-carboxysome assembly initiates when soluble RuBisCO is condensed into a liquid matrix in a pre-carboxysome by the RbcS-like domains of probably both forms of CcmM. CcmN interacts with the N-terminus of full-length CcmM, and then recruits the CcmK major shell protein via CcmN's encapsulation peptide. Shell formation requires CcmK proteins and CcmO. CcmL caps the otherwise elongated carboxysome. Once fully encapsulated carboxysomes are formed, they migrate within the cell probably via interactions with the cytoskeleton. Interacts with full-length and the N-terminal 249 residues of CcmM; a probable CcmM-CcaA-CcmN complex can also be isolated (PubMed:17993516). Interacts with CcmK (By similarity). This cyanobacterium makes beta-type carboxysomes. Belongs to the CcmN family.