The carbon metabolism‐controlled <i>Synechocystis gap2</i> gene harbours a conserved enhancer element and a Gram‐positive‐like −16 promoter box retained in some chloroplast genes

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Abstract

<jats:p>The two glyceraldehyde‐3‐phosphate dehydrogenase‐encoding genes (<jats:italic>gap</jats:italic>) of <jats:italic>Synechocystis</jats:italic> were shown to be expressed as monocistronic transcripts. Whereas <jats:italic>gap1</jats:italic> expression is slow and weak, <jats:italic>gap2</jats:italic> gene induction is rapid and strong. Transcription of the <jats:italic>gap2</jats:italic> gene was shown to depend on functional photosynthetic electron transport and on active carbon metabolism. The basal promoter of <jats:italic>gap2</jats:italic> (P, −45 to +34, relative to the transcription start site) is controlled by three <jats:italic>cis</jats:italic>‐acting elements designated A (−443 to −45), B (+34 to +50, in the untranslated leader region) and C (+50 to +167, in the coding region) that, together, promote a 100‐fold stimulation of P activity. Element B was found to behave as a transcriptional enhancer, in that it was active regardless of its position, orientation and distance relative to P. All three <jats:italic>cis</jats:italic>‐acting stimulatory elements exhibit a common 5′‐agaTYAACg‐3′ nucleotide motif that appears to be conserved in cyanobacteria and may be the target for a transcriptional enhancer. We also report that <jats:italic>gap2</jats:italic> transcription depends on a Gram‐positive‐like −16 promoter box (5′‐TRTG‐3′) that was obviously conserved throughout the evolution of chloroplasts. This is the first report on the occurrence of a −16 promoter element in photoautotrophic organisms.</jats:p>

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