  Relative lifetimes of inherent double stranded DNA openings with lengths up
to ten base pairs are presented for different gene promoters and corresponding
mutants that either increase or decrease transcriptional activity, in the
framework of the Peyrard-Bishop-Dauxois model. Extensive microcanonical
simulations are used, with energies corresponding to physiological temperature.
The bubble lifetime profiles along the DNA sequences demonstrate a significant
reduction of the average lifetime at the mutation sites when the mutated
promoter decreases transcription, while a corresponding enhancement of the
bubble lifetime is observed in the case of mutations leading to increased
transcription. The relative difference of bubble lifetimes between the mutated
and the wild type promoters at the position of mutation varies from 20% to more
than 30% as the bubble length is decreasing
