enzyme components protein L, protein N and protein B are all transcribed constitutively independent of illumination and presence of glucose. Steady-state amounts of proteins in the light-grown cells are two- to threefold greater than in dark-grown cells. Approximately the same amount of protein is present in cultures grown mixtrophically or heterotrophically both containing glucose. Much less protein is present in photoautotrophic cells. Therefore light-independent enzyme activity depends on post-transcriptional and post-translational regulation and switches on both in light and dark