A STATIONARY-PHASE PROTEIN OF ESCHERICHIA-COLI THAT AFFECTS THE MODE OF ASSOCIATION BETWEEN THE TRP REPRESSOR PROTEIN AND OPERATOR-BEARING DNA

Highly purified preparations of trp repressor (TrpR) protein derived f rom Escherichia coli strains that were engineered to overexpress this material were found to contain another protein, of 21 kDa. The second protein, designated WrbA [for tryptophan (W) repressor-binding protein ] remained associated with its namesake through several sequential pro tein fractionation steps. The N-terminal amino acid sequence of the Wr bA protein guided the design of two degenerate oligonucleotides that w ere used as probes in the cloning of the wrbA gene (198 codons). The W rbA protein, in purified form, was found by several criteria to enhanc e the formation and/or stability of noncovalent complexes between TrpR holorepressor and its primary operator targets. The formation of an o perator-holorepressor-WrbA ternary complex was demonstrated by gel mob ility-shift analysis. The WrbA protein alone does not interact with th e trp operator. During the stationary phase, cells deficient in the Wr bA protein were less efficient than wild type in their ability to repr ess the trp promoter. It is proposed that the WrbA protein functions a s an accessory element in blocking TrpR-specific transcriptional proce sses that might be physiologically disadvantageous in the stationary p hase of the bacterial life cycle.