  Over the last several decades it has been increasingly recognized that
stochastic processes play a central role in transcription. Though many
stochastic effects have been explained, the source of transcriptional bursting
(one of the most well-known sources of stochasticity) has continued to evade
understanding. Recent results have pointed to mechanical feedback as the source
of transcriptional bursting but a reconciliation of this perspective with
preexisting views of transcriptional regulation is lacking. In this letter we
present a simple phenomenological model which is able to incorporate the
traditional view of gene expression within a framework with mechanical limits
to transcription. Our model explains the emergence of universal properties of
gene expression, wherein the lower limit of intrinsic noise necessarily rises
with mean expression level.
