* To whom correspondence should be addressed.
Received January 17, 2008; Revision received March 13, 2008
In the absence of exogenous polyamines, the polyamine-deficient Escherichia coli mutant shows not only a characteristic dual-phase growth with abnormal growth, growth arrest, and normal growth after mutation, but also a higher expression of the SOS genes than the polyamine-proficient wild type. The interval of the growth arrest is inversely regulated in a polyamine concentration-dependent manner. These results indicate that the polyamines can act as a signal not only for provoking an adaptive mutation, but also for hastening generation of an adaptive mutation.
KEY WORDS: adaptive mutation, Escherichia coli, mutational speed, polyamine, SOS response