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

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 factor. Our current work indicated that dpsA transcription is also important under metal-ion limitation, because dpsA mRNA levels increased 12-fold under low-iron conditions, and that dpsA function is essential for growth under iron-limiting conditions. Promoter activity of the dpsA-promoter-lacZ reporter gene constructs implied that a region of dyad symmetry centered 28 nucleotides from the transcription start is required for metal-dependent repression, as judged by the level of lacZ induction following treatment of cultures with the chelator 2,2'-dipyridyl. This potential operator sequence is distinct from the site recognized by the cyanobacterial Fur repressor homologue. No other nutrient stresses (nitrogen, sulfur, phosphorus) yielded the high level of induction seen following chelator treatment. These studies suggest that there may be more than one class of metal-dependent repressor in cyanobacteria.