The carbon metabolism-controlled Synechocystis gap2 gene harbours a conserved enhancer element and a Gram-positive-like-16 promoter box retained in some chloroplast genes

The two glyceraldehyde-3-phosphate dehydrogenase-encoding genes (gap) of Sy nechocystis were shown to be expressed as monocistronic transcripts. Wherea s gap1 expression is slow and weak, gap2 gene induction is rapid and strong . Transcription of the gap2 gene was shown to depend on functional photosyn thetic electron transport and on active carbon metabolism. The basal promot er of gap2 (P, -45 to +34, relative to the transcription start site) is con trolled by three cis-acting elements designated A (-443 to -45), B (+34 to +50, in the untranslated leader region) and C (+50 to +167, in the coding r egion) that, together, promote a 100-fold stimulation of P activity. Elemen t B was found to behave as a transcriptional enhancer, in that it was activ e regardless of its position, orientation and distance relative to P. All t hree cis-acting stimulatory elements exhibit a common 5'-agaTYAACg-3' nucle otide motif that appears to be conserved in cyanobacteria and may be the ta rget for a transcriptional enhancer. We also report that gap2 transcription depends on a Gram-positive-like -16 promoter box (5'-TRTG-3') that was obv iously conserved throughout the evolution of chloroplasts. This is the firs t report on the occurrence of a -16 promoter element in photoautotrophic or ganisms.