 Anti-sigma factors are antagonists to the sigma factors, which regulate numerous cell processes including flagellar production, stress response, transport and cellular growth.For example, anti-sigma factor 70 Rsd in "E. coli" is present in the stationary phase and blocks the activity of sigma factor 70 which in essence initiates gene transcription.This allows the sigma S factor to associate with RNA polymerase and direct the expression of the stationary genes.