Growth phase and metal-dependent regulation of the dpsA gene in Synechococcus sp strain PCC 7942

The Synechococcus sp. strain PCC 7942 dpsA gene encodes a stress-inducible DNA-binding protein whose transcription increases in the stationary phase. Such transcription is likely under the control of an alternative sigma fact or. Our current work indicated that dpsA transcription is also important un der metal-ion limitation, because dpsA mRNA levels increased 12-fold under low-iron conditions, and that dpsA function is essential for growth under i ron-limiting conditions. Promoter activity of the dpsA-promoter-lacZ report er gene constructs implied that a region of dyad symmetry centered 28 nucle otides from the transcription start is required for metal-dependent repress ion, as judged by the level of lacZ induction following treatment of cultur es with the chelator 2,2'-dipyridyl. This potential operator sequence is di stinct from the site recognized by the cyanobacterial Fur repressor homolog ue. No other nutrient stresses (nitrogen, sulfur, phosphorus) yielded the h igh level of induction seen following chelator treatment. These studies sug gest that there may be more than one class of metal-dependent repressor in cyanobacteria.