Transcriptional regulation of the circadian clock operon kaiBC by upstream regions in cyanobacteria

Mol Microbiol. 2005 Sep;57(5):1474-84. doi: 10.1111/j.1365-2958.2005.04781.x.


In the cyanobacterium, Synechococcus elongatus PCC 7942, the kaiBC operon is upregulated by the KaiA protein and downregulated by the KaiC protein to generate circadian oscillation. We investigated the regulation of kaiBC transcription. A primer extension and deletion analyses of the upstream region mapped the sufficient promoter region (SPR) to base pairs -55 to +1 (the transcription start site, TSS) and identified a constitutive negative regulatory region upstream of the SPR (base pairs -897 to -56) that extended into the coding sequence of kaiA. Base-pair substitution within the SPR identified a sequence from -52 to -28 that was the essential element for transcription. Most of the examined sequences drove rhythmic expression of a luxAB reporter that was similar to the expression driven by the kaiBC promoter (PkaiBC) and responded to the overexpression of kaiA or kaiC, even in a promoter activity range of 1-8000%. These results indicate that circadian feedback regulation by KaiA and KaiC is addressed to a global step preceding transcription driven by PkaiBC. However, increasing or decreasing the intrinsic activity of PkaiBC greatly affected the rhythm, suggesting that constitutive adjustment of PkaiBC activity by the sequences identified here is essential for the oscillator.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Circadian Rhythm / genetics*
  • Circadian Rhythm Signaling Peptides and Proteins
  • DNA Mutational Analysis
  • Feedback, Physiological / genetics
  • Gene Expression Regulation, Bacterial*
  • Genes, Reporter / genetics
  • Luciferases / analysis
  • Luciferases / genetics
  • Molecular Sequence Data
  • Operon*
  • Promoter Regions, Genetic
  • Sequence Deletion
  • Synechococcus / genetics*
  • Transcription, Genetic


  • Bacterial Proteins
  • Circadian Rhythm Signaling Peptides and Proteins
  • KaiA protein, cyanobacteria
  • KaiB protein, cyanobacteria
  • KaiC protein, cyanobacteria
  • Luciferases