Consequences of Irreversibility in Fundamental Models of Transcription

The ability to watch biochemical events play out at the single-molecule level has led to the discovery that transcription occurs in a noisy, ``bursty'' manner. Recently, as the single-molecule lens is placed over a larger number of organisms and genes, relationships between mean expression and noise beyond the ``bursty'' paradigm have emerged. Through a master-equation formulation of transcription we have found that many powerful physical principles relating to irreversibility seem to play a central role in the newly uncovered trends. Specifically, the relationships between mean expression and noise appears to be a direct consequence of network currents. We discuss how emphasizing the underlying principles in the models can explain recent experimental data and lead to a generalized view of transcription.