Figure 2.

Bursting or nonbursting gene activity, the two types of transcription dynamics of a promoter. A continuum between the two extreme situations portrayed here can be found for different genes. (a) The amount of nascent RNA produced at the promoter fluctuates around a given positive value. The RNA PolII initiates transcription at an average constant rate. The promoter is active and nonbursting. (b) The activity of the promoter (measured as the amount of nascent RNA produced at a given time) alternates between periods of strong production (bursts) and periods of inactivity. The promoter is bursting. The characteristics of a bursting promoter include the frequency of the bursts, the intensity of the bursts, and their duration.31, 32