SmtB is a metal-dependent repressor of the cyanobacterial metallothionein gene smtA: identification of a Zn inhibited DNA-protein complex

The smt locus of Synechococcus PCC 7942 contains a metal-regulated gene (smtA), which encodes a class II metallothionein, and a divergently transcribed gene, smtB, which encodes a repressor of smtA transcription. Regions containing cis-acting eiements required for efficient induction, and required f...

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Bibliographic Details
Published in:Nucleic acids research 1993-02, Vol.21 (4), p.921-925
Main Authors: Morby, Andrew P., Turner, Jennifer S., Huckle, James W., Robinson, Nigel J.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Bacterial Proteins - metabolism
Base Sequence
beta-Galactosidase - genetics
Biological and medical sciences
Cyanobacteria
Cyanophyta
DNA-Binding Proteins - physiology
Fundamental and applied biological sciences. Psychology
Metallothionein - genetics
Molecular and cellular biology
Molecular genetics
Molecular Sequence Data
Operator Regions, Genetic - physiology
Promoter Regions, Genetic - physiology
Repressor Proteins - physiology
Sequence Deletion
Sequence Homology, Amino Acid
Synechococcus
Transcription. Transcription factor. Splicing. Rna processing
Zinc - physiology
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Summary:The smt locus of Synechococcus PCC 7942 contains a metal-regulated gene (smtA), which encodes a class II metallothionein, and a divergently transcribed gene, smtB, which encodes a repressor of smtA transcription. Regions containing cis-acting eiements required for efficient induction, and required for smtB-dependent repression, of the smtA operator-promoter were identified. Specific interactions between proteins extracted from Synechococcus PCC 7942 and defined regions surrounding the smtA operator-promoter were detected by electrophoretic mobility shift assays. Three metallothionein operator-promoter associated complexes were identified, one of which (MAC1) showed Zn-dependent dissociation and involved a region of DNA immediately upstream of smtA. Treatment with Zn-chelators facilitated re-association of MAC1 in vitro. MAC1 was not observed in extracts from smt deficient mutants but was restored in extracts from mutants complemented with a plasmid borne smtB. SmtB is thus required for the formation of a Zn-responsive complex with the smt operator-promoter and based upon the predicted structure of SmtB we propose direct SmtB-DNA interaction exerting metalion inducibie negative control.
ISSN:0305-1048
1362-4962
DOI:10.1093/nar/21.4.921