Circadian Oscillator

Structural Insights into a Circadian Oscillator
Science 31 October 2008 p697

This particular piece concerns the structures and components by which cells keep time. It is not necessarily time as much as rhythmic milestones.

Endogenous (produced from growth of deep tissue) circadian system in cyanobacteria control processes. A circadian rhythm is by definition endogendous and refers to a roughly 24 hour cycle. This machinery can be reconstructed just with proteins KaiA, KaiB, and KaiC. They work through conformational changes and phosphorylation (of what). The mechanism can be deduced as a racheting mechanism and ticks unidirectionally.

Biological processes are dictated by daily, self-sustaining circadian clocks of 24 hour cycles. They show a difference for day and night mediated by dark and light cycles to phase with the environment.

The study concerned prokaryotic cyanobacterium Synechoccus elongates. The rhythm conforms optimally to the daily cycle, including photosynthesis, nitrogen fixation, and gene expression.

This study used competition assays that are…

Any competition assay takes advantage of the fact that that some
signal you can measure depends on the _total_ concentration of
substance. Thus, by introducing a range of _known_ amounts of that
substance and therefore _diluting_ the same substance present in the
sample at unknown concentration, one can extract the number in the
sample.

that demostrate that this clock system significantly enhanced the fitness of the cells in rhythmic environments, but not in non-selective environments.

Clocks have been seen to influence:
- the topology of the entire cyanobacterial chromosome
- the superhelical status of DNA, such as large scale torsion that modulates transcription rates. Therefore, gene-expression patterns are mediated by caily changes in the topology of the gene.
- The chromosome might be envisioned as an oscillating nucleoid that regulates all promoter.
- KaiABC controls the phosphorylation status of RpaA that is a down transcriptional regulator. This is the SasA/RpaA two-component system mediating signals from KaiABC.

Thioredoxin- Thioredoxins are proteins that act as antioxidants by facilitating the reduction of other proteins by cysteine thiol-disulfide exchange.

Phosporylation occurs on the serine and theronine.

Triclosan

Triclosan is the most common chemical in antibacterial products. Genetic mutations can arise in bacteria exposed to triclosan. Triclosan and its close chemical relative triclocarban have been found in 60% of US streams and rivers (Rolf Halden-John Hopkins Bloomberg School of Public Health). Triclosan has been found in human breast milk and blood plasma. It can comprise the hormone system. Scientific American Februaru 200 8 page 96.Triclosan is alcohol soluable and is comprised of phenols, which have antibacterial properties. It is a biocide, with cytoplasm and membrane targets.