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Unusual regulatory elements for iron deficiency induction of the idiA gene of Synechococcus elongatus PCC 7942.
- Source :
-
Journal of bacteriology [J Bacteriol] 2001 Sep; Vol. 183 (17), pp. 5015-24. - Publication Year :
- 2001
-
Abstract
- Expression of a thylakoid membrane-associated protein called IdiA (iron-deficiency-induced protein A) is highly elevated and tightly regulated by iron limitation in Synechococcus elongatus PCC 6301 and PCC 7942. Although this protein is not essential for photosystem II (PSII) activity, it plays an important role in protecting the acceptor side of PSII against oxidative damage, especially under iron-limiting growth conditions, by an unknown mechanism. We defined the iron-responsive idiA promoter by using insertional inactivation mutagenesis and reporter gene assays. A 67-bp DNA region was sufficient for full iron deficiency-inducible idiA promoter activity. Within this fragment is a palindromic sequence 4 bp upstream of a putative -35 promoter element, which resembles the binding site of FNR/CAP-type helix-turn-helix transcription factors. The absence of this palindromic sequence or a 3-bp mutation in a putative -10 region eliminated promoter activity completely. A previously identified candidate for a positively acting transcription factor is the IdiB protein, whose gene lies immediately downstream of idiA. IdiB shows strong similarity to helix-turn-helix transcription factors of the FNR/CAP family. A His(6x)-tagged IdiB that was overexpressed in Escherichia coli bound to a 59-bp fragment of the idiA regulatory region that included the palindrome. Although the idiA promoter lacks a consensus binding site for the iron-sensing regulator Fur, we attempted to inactivate fur in order to investigate the potential role of this factor. The resulting merodiploid mutants showed constitutive partial derepression of IdiA expression under iron-sufficient growth conditions. We concluded that IdiB is a specific iron-responsive regulator of idiA and that Fur has an indirect role in influencing idiA expression.
- Subjects :
- Chromosome Mapping
DNA, Bacterial chemistry
Electrophoresis, Polyacrylamide Gel
Oxidative Stress
Photosynthetic Reaction Center Complex Proteins
Photosystem II Protein Complex
Promoter Regions, Genetic
Sequence Analysis, DNA
Sigma Factor genetics
Transcription Factors metabolism
Bacterial Proteins
Carrier Proteins genetics
Cyanobacteria genetics
Iron Deficiencies
Iron-Binding Proteins
Transcription Factors genetics
Subjects
Details
- Language :
- English
- ISSN :
- 0021-9193
- Volume :
- 183
- Issue :
- 17
- Database :
- MEDLINE
- Journal :
- Journal of bacteriology
- Publication Type :
- Academic Journal
- Accession number :
- 11489854
- Full Text :
- https://doi.org/10.1128/JB.183.17.5015-5024.2001