In the cyanobacterium Synechococcus sp. PCC 7942, the photosystem II reaction center protein D1 is encoded by three psbA genes. The psbAI gene encodes the D1:1 protein that is the prevailing form under steady state conditions, whereas the expression of the psbAII and psbAIII genes, encoding the D1:2 protein, is enhanced under many stress conditions. Here, we show that in addition to transcriptional control, the synthesis of D1 protein forms is regulated at the levels of membrane targeting of psbA mRNA ribosome complexes and translation elongation, whereas the formation of translation initiation complexes does not have a significant regulatory role.
Copyright 2004 Elsevier B.V.