Induction of gamma delta transposition in response to elevated glucose-6-phosphate levels.

The nonenzymatic glycosylation of nucleic acids in vitro by the reducing sugars, glucose or glucose-6-phosphate, alters both physical and biological properties. Recent investigations have demonstrated that elevated intracellular levels of glucose-6-phosphate in glycolytic mutants of E. coli resulted in a concentration-associated increase in mutations of a target plasmid. The majority of the plasmid mutations were due to large (greater than 1 kb) insertions or deletions. We describe here the further analysis of mutant plasmids isolated from bacteria grown under conditions which were conducive to the intracellular accumulation of glucose-6-phosphate. We have found that a number of the insertional plasmid mutations were the result of the movement of the transposable element gamma delta from the host genome into the plasmid. The frequency of gamma delta transposition was also associated with the amount of glucose-6-phosphate accumulated in the bacterial cells. Furthermore, the presence of another transposable element, either Tn 5 or Tn 10 in the host genome increased the rate of gamma delta transposition without affecting its own movement. The observed increase in gamma delta transposition suggests a novel mechanism of induction by reducing sugars which may be the result of DNA modifications by reducing sugars.