Tanenbaum, M.E. et al. Cell 159, 635–646 (2014).

The ability to amplify signals can be useful in a variety of biological contexts, such as in increasing transcription or improving fluorescence imaging. Tanenbaum et al. developed a protein tag that achieves such amplification. Their SunTag consists of up to 24 copies of a GCN4-derived peptide that bind multiple copies of specific single-chain antibodies. These antibodies can be fused to GFP for protein imaging purposes or to a Cas9 transcriptional activator for transcriptional applications. As the SunTag recruits up to 24 copies of GFP or Cas9, strong fluorescence or high transcriptional activity can be obtained. The researchers demonstrated this signal amplification in single-molecule imaging of motor, cytoplasmic, membrane-bound and mitochondria-associated proteins as well as for activating the overexpression of a chemokine receptor.