Poster: Late and Moved Abstracts

Abs # 1394: The LysR family protein, CmpR, regulates transcription of low-CO₂ and high-light responsive genes in the cyanobacterium Synechococcus sp. strain PCC 7942

Presenter:	Takahashi, Yukari , i002008d@mbox.nagoya-u.ac.jp
Authors	Takahashi, Yukari  (A)   Yamaguchi, Osamu  (A)   Omata, Tatsuo  (A)
Affiliations:	(A): Graduate School of Bioagricultural Sciences, Nagoya University

Transcription of the cmpABCD operon of the cyanobacterium Synechococcus sp. strain PCC 7942, encoding a high-affinity bicarbonate transporter, is induced under low CO₂ conditions by a LysR-type transcriptional regulator CmpR. Transcription of the operon was induced also by transfer of the cells from low-light (30 microeinsteins m^-2S^-1) to high-light (120 microeinsteins m^-2S^-1) conditions under air level of CO₂ as reported previously by Reddy et al., and the light-responsive induction was found to be abolished by inactivation of cmpR, indicating that the high-light induction and low-CO₂ induction of the operon are essentially the same phenomenon at the molecular level. Expression of the high-light inducible genes psbAII and psbAIII, on the other hand, was found to be induced by CO₂ limitation at a constant light intensity of 70 microeinsteins m^-2S^-1, indicating that these genes also sense CO₂ limitation and high-light by a common mechanism. CmpR was, however, not required for induction of psbAII and psbAIII, indicating involvement of other transcriptional regulator(s) in induction of these genes. The CmpR mutant nevertheless showed reduced levels of the psbAII and psbAIII transcripts as compared to the wild-type levels under the light and CO₂ conditions examined. Gel shift assays showed that CmpR binds to the previously identified enhancer elements of psbAII and psbAIII, through specific interaction with a sequence signature conforming to the binding motif of the related LysR-family proteins, TTA-N_7/8-TAA. These findings suggested that CmpR binds to the enhancer elements in vivo and thereby increases the transcription levels of psbAII and psbAIII.