IGEM:Harvard/2006/Brainstorming Papers - Zhipeng

Cyanobacteria

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Kondo et al.

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Circadian organization (Kondo et al 2004).

• gene cluster KaiABC involved
• no homology to eukarayotic circadian systems
• Central oscillator controls output patterns; phase of oscillator controlled by input
• Photosynthesis by day, nitrogen fixation by night (2 incompatible in unicellular)
• Used luciferase DNA expressed downstream as a reporter
• Genome 2.7kb in size (e. coli 6.1kb)
• Put luxAB on a psbA plasmid, luxAB luciferase related protein  volatile
  • See diagram in paper for circuitry
• KaiABC system
  • Overexpression of KaiC represses KaiA and KaiB
  • Overexpression of KaiA activates KaiBC
  • KaiC center of oscillation
• Question TBA: why 24h period?
  • Single point mutations in KaiC can change period from 14h to 60h
• Drosophila and Neurospora also have clock models
• Cyanobacteria has no nuclear envelope, can divide 6h/time
• KaiABC analogues only found on archaeobacteria

Kucho et al.

• Purpose of regulation to prepare cell for night in cyanobacteria
• Tested Synechocystis, which is a different strain of cyanobacteria
• 77% in Synechocystis rhymic clones; 100% in Synechococcus
• In cyanobacteria
  • KaiC regulated by negative feedback autoreg. loop
  • KaiA activates kaiBC
• Used DNA microarray to determine mRNA cyclic nature
• cycling genes detected; peak expression from day to night
  • Genes mostly:
    • unassigned
    • carbohydrate metabolism
    • energy metabolism purposes
    • transcription!
    • translation!
• 2 Sigma factors have circadian rhythm: sll1689, sll0687 on RNAPol

Other

• (Wikipedia)Cyanobacteria are the only group of organisms that are able to reduce nitrogen and carbon in aerobic conditions