BMC-like domains exist in cyanobacteria, proteobacteria, and actinobacteria and are homologs of the carboxysome shell proteins. They might be encoded from putative organelles involved in unknown metabolic process. Although it has been suggested that these carboxysome shell protein homologs form hexamers and further assemble into the flat facets of the polyhedral bacterial organelles shell at present no experimental evidence exists to directly support this view. Proteins in this CD contain two tandem BMC domains. This CD includes repeat 1 (the first BMC domain of BMC like 1 proteins).