Heat shock transcription factor δ32 is targeted for degradation via an ubiquitin-like protein ThiS in Escherichia coli

The posttranslational modification of proteins with ubiquitin and ubiquitin-like proteins (UBLs) plays an important role in eukaryote biology, through which substrate proteins are targeted for degradation by the proteasome. Prokaryotes have been thought to degrade proteins by an ubiquitin independent pathway. Here, we show that ThiS, an ubiquitin-like protein, is covalently attached to δ32 and at least 27 other proteins, leading to their subsequent degradation by proteases, in a similar manner to the ubiquitin-proteasome system (UPS) in eukaryotes. Molecular biology and biochemical studies confirm that specific lysine sites in δ32 can be modified by ThiS. The results presented here establish a new model for δ32 degradation and show that Escherichia coli uses a small-protein modifier to control protein stability.