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Journal of Bacteriology, December 2000, p. 6592-6597, Vol. 182, No. 23
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Unphosphorylated Receiver Domain of PhoB Silences the Activity of Its Output Domain

Damon W. Ellison and William R. McCleary*

Microbiology Department, Brigham Young University, Provo, Utah 84602-5253

Received 17 July 2000/Accepted 18 September 2000

PhoB is the response regulator of the Pho regulon. It is composed of two distinct domains, an N-terminal receiver domain and a C-terminal output domain that binds DNA and interacts with sigma 70 to activate transcription of the Pho regulon. Phosphorylation of the receiver domain is required for activation of the protein. The mechanism of activation by phosphorylation has not yet been determined. To better understand the function of the receiver domain in controlling the activity of the output domain, a direct comparison was made between unphosphorylated PhoB and its solitary DNA-binding domain (PhoBDBD) for DNA binding and transcriptional activation. Using fluorescence anisotropy, it was found that PhoBDBD bound to the pho box with an affinity seven times greater than that of unphosphorylated PhoB. It was also found that PhoBDBD was better able to activate transcription than the full-length, unmodified protein. We conclude that the unphosphorylated receiver domain of PhoB silences the activity of its output domain. These results suggest that upon phosphorylation of the receiver domain of PhoB, the inhibition placed upon the output domain is relieved by a conformational change that alters interactions between the unphosphorylated receiver domain and the output domain.

* Corresponding author. Mailing address: Microbiology Department, Brigham Young University, 775 WIDB, Provo, UT 84602-5253. Phone: (801) 378-8793. Fax: (801) 378-9197. E-mail: bill_mccleary{at}byu.edu.

Journal of Bacteriology, December 2000, p. 6592-6597, Vol. 182, No. 23
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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