Transcription Activation via Transcriptional Bursting

Abstract

Transcription factors (TFs) often regulate their own expression; monitoring TF production in real time will help elucidate autoregulatory mechanisms. However, many TFs are expressed at low levels and are difficult to detect. Further, labeling TFs with fluorescent proteins risks disrupting their regulatory functions. Here, we report a novel strategy, Co-Translational Activation by Cleavage (CoTrAC), to monitor autoregulation of a transcription factor, λ repressor cI, in live E. coli cells. CI becomes fully functional upon co-translational cleavage from a membrane-targeted fluorescent reporter, which can be counted individually. Using this strategy, we discovered that cI activates its own expression via transcriptional bursting_the production of multiple mRNA molecules in brief, well-separated periods of time. CI increases not only the frequency but also the size of transcriptional bursts. Negative autoregulation by cI decreases the burst frequency, but not the burst size. These results link activation of gene expression by a TF to burst-like transcription.