Organization and expression of nitrogen-fixation genes in the aerobic nitrogen-fixing unicellular cyanobacterium Synechococcus sp. strain RF-1

Huang, Tan-Chi; Lin, Rong-Fong; Chu, Mu-Kuei; Chen, Horng-Ming

doi:10.1099/13500872-145-3-743

Cited by 57 publications

(42 citation statements)

References 18 publications

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“…In a unicellular nitrogen-fixing strain, Cyanothece sp. strain PCC 8801, transcription start sites were identified upstream of nifE, nifX, and nifW (48), so it seemed likely that there would be a promoter upstream of nifE1 in A. variabilis. To determine whether the nifEN1 genes had their own promoter, we constructed fusions of various-size fragments upstream of nifE1 to a promoterless lacZ (Fig.…”

Section: Resultsmentioning

confidence: 99%

Regulation of Nitrogenase Gene Expression by Transcript Stability in the Cyanobacterium Anabaena variabilis

Pratte

Thiel

2014

Journal of Bacteriology

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The nitrogenase gene cluster in cyanobacteria has been thought to comprise multiple operons; however, in Anabaena variabilis, the promoter for the first gene in the cluster, nifB1, appeared to be the primary promoter for the entire nif cluster. The structural genes nifHDK1 were the most abundant transcripts; however, their abundance was not controlled by an independent nifH1 promoter, but rather, by RNA processing, which produced a very stable nifH1 transcript and a moderately stable nifD1 transcript. There was also no separate promoter for nifEN1. In addition to the nifB1 promoter, there were weak promoters inside the nifU1 gene and inside the nifE1 gene, and both promoters were heterocyst specific. In an xisA mutant, which effectively separated promoters upstream of an 11-kb excision element in nifD1 from the downstream genes, the internal nifE1 promoter was functional. Transcription of the nif1 genes downstream of the 11-kb element, including the most distant genes, hesAB1 and fdxH1, was reduced in the xisA mutant, indicating that the nifB1 promoter contributed to their expression. However, with the exception of nifK1 and nifE1, which had no expression, the downstream genes showed low to moderate levels of transcription in the xisA mutant. The hesA1 gene also had a promoter, but the fdxH gene had a processing site just upstream of the gene. The processing of transcripts at sites upstream of nifH1 and fdxH1 correlated with increased stability of these transcripts, resulting in greater amounts than transcripts that were not close to processing sites.

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Section: Resultsmentioning

confidence: 99%

Regulation of Nitrogenase Gene Expression by Transcript Stability in the Cyanobacterium Anabaena variabilis

Pratte

Thiel

2014

Journal of Bacteriology

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“…Temporal separation may be the original drive for the evolution of circadian clocks. Like purF, nitrogenase genes are expressed at night in unicellular diazatrophic cyanobacteria (12,15,29). The products of these genes are sensitive to O 2 , which is produced by photosynthesis during the (subjective) day.…”

Section: Discussionmentioning

confidence: 99%

A New Circadian Class 2 Gene, opcA , Whose Product Is Important for Reductant Production at Night in Synechococcus elongatus PCC 7942

Huang

Golden

2000

J Bacteriol

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Gene expression in the cyanobacterium Synechococcus elongatus PCC 7942 is under the control of a circadian oscillator, such that peaks and troughs of expression recur with a periodicity of about 24 h in the absence of environmental cues. This can be monitored easily as light production from luciferase gene fusions to S. elongatus promoters. All promoters seem to exhibit circadian oscillation of expression, but the phasing of peak and trough times differs among different genes. The majority of genes are designated class 1, with expression peaks near dusk or subjective dusk (the time corresponding to dusk in the absence of a diurnal cycle). A minority, of which purF is an example, have expression peaks approximately 12 h out of phase with class 1 genes. A screen of Tn5 mutants for those in which purF phasing is altered revealed a mutant that carries an insertion in the opcA gene, previously identified as essential for glucose-6-phosphate dehydrogenase function. However, a different enzymatic reporter and in vitro luciferase assays revealed that the expression pattern of the purF promoter is not altered by opcA inactivation, but rather the reduced flavin mononucleotide substrate of luciferase is limiting at the time of the natural circadian peak. The results suggest that OpcA is involved in temporally separated reductant-generating pathways in S. elongatus and that it has a role outside of its function in activating glucose-6-phosphate dehydrogenase. The opcA gene, expected to be cotranscribed with fbp and zwf, was shown to have its own class 2 promoter, whereas the fbp promoter was determined to be in class 1. Thus, opcA expression is likely to be constitutive by virtue of the activity of two promoters in nearly opposite circadian phases.

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“…This observation suggests that circadian cycles allow cellular processes to occur in a temporal sequence that is most beneficial to the organism. For example, some species of cyanobacteria (e.g., the genera Trichodesmium, Cyanothece, and Synechococcus) show a daily rhythm of photosynthesis that is in reverse phase to the daily cycle of nitrogenase expression, a key enzyme for nitrogen fixation Schneegurt et al, 1994;Huang et al, 1999). The peak of nitrogenase expression is during the dark phase of the cycle, allowing the temporal separation of expression of the oxygen-sensitive nitrogenase enzyme during periods when oxygen-evolving photosynthesis is not occurring.…”

Section: Rhythmic Clock Outputs In Cyanobacteriamentioning

confidence: 99%

No Promoter Left Behind: Global Circadian Gene Expression in Cyanobacteria

Woelfle

Johnson

2006

J Biol Rhythms

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Prokaryotic cyanobacteria express robust circadian (daily) rhythms under the control of a clock system that appears to be similar to those of eukaryotes in many ways. On the other hand, the KaiABC-based core cyanobacterial clockwork is clearly different from the transcriptiontranslation feedback loop model of eukaryotic clocks in that the cyanobacterial clock system regulates gene expression patterns globally, and specific clock gene promoters are not essential in mediating the circadian feedback loop. A novel model, the oscilloid model, proposes that the KaiABC oscillator ultimately mediates rhythmic changes in the status of the cyanobacterial chromosome, and these topological changes underlie the global rhythms of transcription. The authors suggest that this model represents one of several possible modes of regulating gene expression by circadian clocks, even those of eukaryotes. Keywords circadian; biological clock; kai; prokaryote; global gene expression; supercoiling Animals, plants, fungi, and cyanobacteria all display daily or circadian rhythms in their biochemistry, physiology, and/or behavior that are controlled by biological clocks (Dunlap et al., 2004). A variety of biological processes in various organisms are controlled by biological clocks such as gene expression, photosynthesis, sleeping/waking, and development, and this regulation is thought to help organisms adapt to the daily changes in light, temperature, and other factors in their environment. Circadian regulation of gene expression (i.e., the levels of specific proteins in cells) can be accomplished by clock control of transcription, mRNA stability, translation, and protein degradation. A particularly fascinating example of translational control by a circadian clock is that in the dinoflagellate alga, Gonyaulax (Rossini et al., 2003). However, we focus our discussion specifically on clock control of cyanobacterial gene expression at the level of transcription.In general, studies of circadian gene expression in eukaryotes have often used microarray analyses to show that a relatively small proportion of genes (~5%-15%) in eukaryotic genomes display rhythms in mRNA abundance. While microarray technology is well advanced, it should be noted that microarrays are not very sensitive to small changes of mRNA abundance, and moreover, they are not a good measure of rhythmic transcriptional activity for mRNAs that are either very unstable or very stable. Therefore, microarray results might not be reflective of transcriptional control in detail.

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Organization and expression of nitrogen-fixation genes in the aerobic nitrogen-fixing unicellular cyanobacterium Synechococcus sp. strain RF-1

Cited by 57 publications

References 18 publications

Regulation of Nitrogenase Gene Expression by Transcript Stability in the Cyanobacterium Anabaena variabilis

Regulation of Nitrogenase Gene Expression by Transcript Stability in the Cyanobacterium Anabaena variabilis

A New Circadian Class 2 Gene, opcA , Whose Product Is Important for Reductant Production at Night in Synechococcus elongatus PCC 7942

No Promoter Left Behind: Global Circadian Gene Expression in Cyanobacteria

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