How does DNA protect itself in conditions of acute starvation or environmental assault? Prof. Avi Minsky of the Weizmann Institute's Organic Chemistry Department has found that, in bacteria, DNA's answer is to "get organized."
During various conditions of stress, Minsky discovered, bacterial DNA becomes remarkably organized into a tightly packed crystalline structure, allowing the bacteria to better withstand environmental stress. "In natural environments, bacterial life alternates between short periods of feast and long periods of famine," says Minsky. "To survive, bacteria have evolved complex mechanisms that allow them to protect themselves during starvation and stress, as well as to resume growth very rapidly when conditions improve. The ordered DNA structure may represent the ultimate mode of protection."
The Weizmann team revealed further that the highly ordered structure is mediated by a protein called Dps, which strongly binds DNA, increasing its stability. The Dps protein, characterized by Prof. Roberto Kolter's group at Harvard Medical School with which Minsky collaborates, is present at high levels in stressed cells. Within this ordered and tightly packed DNA-Dps structure, the DNA is very effectively protected against various assaults.
The scientists used X-ray and electron microscopy techniques, which are currently being employed to uncover the molecular structure of the complex between the Dps protein and the DNA. Says Minsky: "We are currently investigating the actual signal that triggers the formation of the crystalline structure when the organism is subjected to starvation or stress, and the signal that causes its fast disappearance once stress is eliminated."
Other than providing important information on how DNA could be protected, the findings may one day contribute to the development of more general methods against bacterial diseases. In addition, if a link is found between the mechanisms allowing bacteria to survive under stress and those that render bacteria resistant against various chemical agents, chemotherapy could be efficiently used against pathological bacteria that have become resistant to other methods.
Minsky: "Order is generally considered to be incompatible with life. However, in living systems exposed to severe environmental assaults, ordered assemblies may confer an efficient means for wide-range protection. Indeed, ribosomes in brain cells of people suffering from dementia were found to form crystalline organizations. Moreover, DNA in sperm cells is highly ordered. We have now found this to be true in bacterial DNA as well and are trying to understand how general and significant the correlation is between order and survival."
Accordingly, the Weizmann team has recently begun to study the correlation between the organization of DNA and fertility in human sperm cells.