Dynamics of Gene Silencing in a Live Cell: Stochastic Resonance.

Binding of a specific siRNA to the target mRNA in a live cell (human breast cancer cell, MCF-7) is studied by confocal microscopy. The specific siRNA (labeled with a fluorophore, alexa 488) exhibits much higher intensity of fluorescence in the bound state than in the free (unbound) state. It is observed that repeated unbinding and rebinding of siRNA (to target mRNA) occur before gene silencing. 16 273 on-time periods (residence or dwell time of siRNA in bound form) are detected. They follow a strikingly simple pattern. All of the on-time periods are odd-integral multiples of 5.5 ± 0.05 ms. This is ascribed to stochastic resonance.