Gu, L. et al. Nature doi:10.1038/nature13761 (21 September 2014).

Gu et al. bring the power of single-molecule sequencing technology to profile protein interactions with a new approach called single-molecule-interaction sequencing, or SMI-seq. The approach is based on tagging proteins with DNA barcodes that can be read out by sequencing. First, proteins are barcoded with DNA tags by ribosome display or enzymatic conjugation; next, the barcoded proteins are randomly immobilized in a gel matrix; then, the DNA barcodes are amplified into in situ polymerase colonies ('polonies'). Barcoded proteins in a complex mixture can thus be identified and quantified by DNA sequencing, and protein-protein interactions can be detected by sequencing colocalized polonies. Gu et al. demonstrated the utility of this powerful platform for profiling the binding repertoire of an antibody and also for screening for small molecules that mediate G protein–coupled receptor activation.