Nucleic Acids Research, 1989, Vol. 17, No. 14 5517-5528
© 1989
MOLECULAR BIOLOGY |
Up-promoter mutations in the positively-regulated mer promoter of TnSOl

Department of Biochemistry, University of Bristol School of Medical Sciences, University Walk Bristol BS8 1TD, UK
*To whom correspondence should be addressed
Received April 26, 1989. Revised June 15, 1989. Accepted June 15, 1989.
Transcription from the mer promoter of transposon Tn5O1 is repressed by MerR (the product of the merR gene) in the absence of Hg2+, and activated by MerR in the presence of Hg2+. In the absence of MerR, the mer promoter has weak constitutive activity. The DNA sequence of the mer promoter shows candidate -35 and - 10 sequences at the unusually high spacing of 19 base-pairs. We have selected for spontaneous mutations in the mer promoter that confer an up-promoter phenotype. Four different mutants have been isolated. Three of these are single base-pair deletions between the 10 and 35 sequences. A fourth removes the -10 sequence entirely, and places a second potential -10 sequence 17 base-pairs from the -35 sequence. None of these mutant promoters are induced by MerR in the presence of Hg2+. Two of them are repressed by MerR irrespective of the presence or absence of Hg2+. Models for the mode of action of the MerR protein are discussed in the light of these results. Our data support a mechanism in which the MerR protein in the presence of Hg2+ acts to change the conformation of DNA in the mer promoter.
+Present addresses: School of Biological Sciences, University of Birmingham, PO Box 363, Birmingham B15 2TT, UK
Present addresses: Advanced Genetic Science, 6701 San Pablo Avenue, Oakland, CA 94608, USA
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