  Transcriptional repression may cause transcriptional noise by a competition
between repressor and RNA polymerase binding. Although promoter activity is
often governed by a single limiting step, we argue here that the size of the
noise strongly depends on whether this step is the initial equilibrium binding
or one of the subsequent unidirectional steps. Overall, we show that
nonequilibrium steps of transcription initiation systematically increase the
cell-to-cell heterogeneity in bacterial populations. In particular, this allows
also weak promoters to give substantial transcriptional noise.
