A Role for Asp75 in Domain Interactions in the
Bacillus subtilis Response Regulator Spo0A*
Marguerite A.
Cervin
§ and
George B.
Spiegelman¶
From the Department of Microbiology and Immunology
and ¶ Department of Medical Genetics, University of British
Columbia, Vancouver, British Columbia V6T 1Z3, Canada
Spo0A is a two-domain response regulator required
for sporulation initiation in Bacillus subtilis. Studies on
response regulators have focused on the activity of each domain, but
very little is known about the mechanism by which the regulatory domain
inhibits the activator domain. In this study, we created a single amino acid substitution in the regulatory domain, D75S, which resulted in a
dramatic decrease in sporulation in vivo. In vitro studies with the purified Spo0AD75S protein demonstrated that phosphorylation and DNA binding were comparable with wild type Spo0A. However, the
mutant was unable to stimulate transcription by 
A-RNA
polymerase from the Spo0A-dependent spoIIG
operon promoter. We suggest that the amino acid Asp75
and/or the region within which it resides, the 
3-
4 loop, are involved in the inhibitory interaction between the regulatory and
activator domains of Spo0A.
*
This work was supported by a grant from the Medical Research
Council of Canada (to G. B. S.).The costs of publication of this article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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