Dataset Information

Unusual regulatory elements for iron deficiency induction of the idiA gene of Synechococcus elongatus PCC 7942.

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.

SUBMITTER: Michel KP

PROVIDER: S-EPMC95377 | biostudies-literature | 2001 Sep

REPOSITORIES: biostudies-literature

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Unusual regulatory elements for iron deficiency induction of the idiA gene of Synechococcus elongatus PCC 7942.

Michel K P KP Pistorius E K EK Golden S S SS

Journal of bacteriology 20010901 17

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 ...[more]

PMID: 11489854

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Project description:The direct conversion of carbon dioxide into biofuels by photosynthetic microorganisms is a promising alternative energy solution. In this study, a model cyanobacterium, Synechococcus elongatus PCC 7942, is engineered to produce free fatty acids (FFA), potential biodiesel precursors, via gene knockout of the FFA-recycling acyl-ACP synthetase and expression of a thioesterase for release of the FFA. Similar to previous efforts, the engineered strains produce and excrete FFA, but the yields are too low for large-scale production. While other efforts have applied additional metabolic engineering strategies in an attempt to boost FFA production, we focus on characterizing the engineered strains to identify the physiological effects that limit cell growth and FFA synthesis. The strains engineered for FFA-production show reduced photosynthetic yields, chlorophyll-a degradation, and changes in the cellular localization of the light-harvesting pigments, phycocyanin and allophycocyanin. Possible causes of these physiological effects are also identified. The addition of exogenous linolenic acid, a polyunsaturated FFA, to cultures of S. elongatus 7942 yielded a physiological response similar to that observed in the FFA-producing strains with only one notable difference. In addition, the lipid constituents of the cell and thylakoid membranes in the FFA-producing strains show changes in both the relative amounts of lipid components and the degree of saturation of the fatty acid side chains. These changes in lipid composition may affect membrane integrity and structure, the binding and diffusion of phycobilisomes, and the activity of membrane-bound enzymes including those involved in photosynthesis. Thus, the toxicity of unsaturated FFA and changes in membrane composition may be responsible for the physiological effects observed in FFA-producing S. elongatus 7942. These issues must be addressed to enable the high yields of FFA synthesis necessary for large-scale biofuel production.

Dataset Information

Unusual regulatory elements for iron deficiency induction of the idiA gene of Synechococcus elongatus PCC 7942.

Publications

Unusual regulatory elements for iron deficiency induction of the idiA gene of Synechococcus elongatus PCC 7942.

Similar Datasets

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