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Proteolysis of the phage λ CII regulatory protein by FtsH (HflB) of Escherichia coli

Rapid proteolysis plays an important role in regulation of gene expression. Proteolysis of the phage λ CII transcriptional activator plays a key role in the lysis‐lysogeny decision by phage λ. Here we demonstrate that the E. coli ATP‐dependent protease FtsH, the product of the host ftsH/hflB gene, is responsible for the rapid proteolysis of the CII protein. FtsH was found previously to degrade the heat‐shock transcription factor σ32. Proteolysis of σ32 requires, in vivo, the presence of the DnaK‐DnaJ‐GrpE chaperone machine. Neither DnaK‐DnaJ‐GrpE nor GroEL‐GroES chaperone machines are required for proteolysis of CII in vivo. Purified FtsH carries out specific ATP‐dependent proteolysis of CII in vitro. The degradation of CII is at least 10‐fold faster than that of σ32. Electron microscopy revealed that purified FtsH forms ring‐shaped structures with a diameter of 6–7 nm.