There is a new twist on the question of how biological clocks work.
In recent years, scientists have discovered that biological clocks help organize a dizzying array of biochemical processes in the body. Despite a number of hypotheses, exactly how the microscopic pacemakers in every cell in the body exert such a widespread influence has remained a mystery.
Now, a new study provides direct evidence that biological clocks can influence the activity of a large number of different genes in an ingenious fashion, simply by causing chromosomes to coil more tightly during the day and to relax at night.
The idea that the whole genome is oscillating is really cool, enthuses Vanderbilt Professor of Biological Sciences Carl Johnson, who headed the research that was published online Nov. 13 in the Proceedings of the National Academy of Sciences. The fact that oscillations can act as a regulatory mechanism is telling us something important about how DNA works: It is something DNA jockeys really need to think about.
Johnsons team, which consisted of Senior Lecturer Mark A Woelfle, Assistant Research Professor Yao Xu and graduate student Ximing Qin, performed the study with cyanobacteria (blue-green algae), the simplest organism known to possess a biological clock. The chromosomes in cyanobacteria are organized in circular molecules of DNA. In their relaxed state, they form a single loop. But, within the cell, they are usually supercoiled into a series of small helical loops. There are even two families of special enzymes, called gyrases and topoisomerases, whose function is coiling and uncoiling DNA.
The researchers focused on small, non-essential pieces of DNA in the cyanobacteria called plasmids that occur naturally in the cyanobacteria. Because a plasmid should behave in the same fashion as the larger and more unwieldy chromosome, the scientists consider it to be a good proxy of the behavior of the chromosome itself.
When the plasmid is relaxe
|Contact: David F. Salisbury|