CHARACTERIZATION OF CIS-ELEMENTS THAT REGULATE THE EXPRESSION OF GLNAIN SYNECHOCOCCUS SP STRAIN PCC-7942

The upstream noncoding region of the Synechococcus sp. strain PCC 7942 (hereafter referred to as Synechococcus 7942) glnA gene was fused to the cat gene in order to study the expression of glnA both in Synechoc occus 7942 and in Escherichia coli. The lack of cat expression in E. c oli indicated that the glnA promoter was not recognized by E. coli RNA polymerase. The fused construct was integrated into the Synechococcus 7942 chromosome at a neutral site. Expression of the cat reporter gen e was regulated under various nitrogen conditions in a way similar to that of the glnA gene. A deletion introduced at the binding site of th e NtcA regulatory protein abolished derepression of the glnA promoter during growth in nitrate and under nitrogen starvation. Deletion of th e sequence between the transcription and translation start sites of gl nA prevented the repression observed during growth in ammonium. These results indicate that the glnA promoter is subject to complex regulati on that involves sequences upstream and downstream from the transcript ion start site.