|The glycine cleavage system (GCS) is essential for all eukaryotes. It consists of four proteins and converts glycine to serine. Early research from plants showed complex formation of these proteins under high concentrations in vitro but not in vivo. Using the very similar proteins of the GCS from the model cyanobacteria Synechocystis sp. PCC 6803 we analysed if complex formation was possible for organisms other than plants. The analysis showed complex formation of the Synechocystis proteins. Therefore, this GCS can be used as a model for further structure and function analysis.