Purification of the phoU protein, a negative regulator of the pho regulon of Escherichia coli K-12.

Thermally induced transcription of the phoU gene under control of the major leftward promoter, pL, of phage lambda resulted in production of the PhoU protein to compose approximately 5% of the total cell protein. The PhoU protein was present in the cytoplasm in the form of an aggregate. The amino acid composition and N-terminal amino acid sequence of the purified protein confirmed the reading frame established earlier for the phoU gene.