Photosynthetic regulation of the cyanobacterium Synechocystis sp. PCC 6803 thioredoxin system and functional analysis of TrxB (Trx x) and TrxQ (Trx y) thioredoxins.

The expression of the genes encoding the ferredoxin-thioredoxin system including the ferredoxin-thioredoxin reductase (FTR) genes ftrC and ftrV and the four different thioredoxin genes trxA (m-type; slr0623), trxB (x-type; slr1139), trxC (sll1057) and trxQ (y-type; slr0233) of the cyanobacterium Synechocystis sp. PCC 6803 has been studied according to changes in the photosynthetic conditions. Experiments of light-dark transition indicate that the expression of all these genes except trxQ decreases in the dark in the absence of glucose in the growth medium.

Properties of the recombinant ferredoxin-dependent glutamate synthase of Synechocystis PCC6803. Comparison with the Azospirillum brasilense NADPH-dependent enzyme and its isolated alpha subunit.

The properties of the recombinant ferredoxin-dependent glutamate synthase of Synechocystis PCC6803 were determined by means of kinetic and spectroscopic approaches in comparison to those exhibited by the bacterial NADPH-dependent enzyme form. The ferredoxin-dependent enzyme was found to be similar to the bacterial glutamate synthase alpha subunit with respect to cofactor content (one FMN cofactor and one [3Fe-4S] cluster per enzyme subunit), overall absorbance properties, and reactivity of the FMN N(5) position with sulfite, as expected from the similar primary structure of ferredoxin-dependent glutamate synthase and of the bacterial NADPH-dependent glutamate synthase alpha subunit. The ferredoxin- and NADPH-dependent enzymes were found to differ with respect to the apparent midpoint potential values of the FMN cofactor and of the [3Fe-4S] cluster, which are less negative in the ferredoxin-dependent enzyme form.

Electron transport controls transcription of the thioredoxin gene (trxA) in the cyanobacterium Synechocystis sp. PCC 6803.

The trxA gene encoding one of the different thioredoxins of the facultative heterotrophic cyanobacterium Synechocystis sp. PCC 6803 is transcribed as a single mRNA of 450 nucleotides. Transcript accumulation is similar in all standard growth conditions but strongly decreases after transferring cell cultures from light to darkness.

The GS-GOGAT pathway is not operative in the heterocysts. Cloning and expression of glsF gene from the cyanobacterium Anabaena sp. PCC 7120.

The gene encoding the ferredoxin-dependent glutamate synthase (Fd-GOGAT), glsF, from the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120, has been cloned and sequenced. Unlike other cyanobacteria, Anabaena 7120 contains only Fd-GOGAT, lacking NADH-GOGAT.

Ferredoxin-dependent iron-sulfur flavoprotein glutamate synthase (GlsF) from the Cyanobacterium synechocystis sp. PCC 6803: expression and assembly in Escherichia coli.

The unicellular cyanobacterium Synechocystis sp. PCC 6803 contains two different glutamate synthases whose genes, gltB and glsF (previously known as gltS), have been cloned (F. Navarro et al.

Telomeric silencing of a natural subtelomeric gene.

The heterochromatin at telomeres can repress the expression of reporter genes when they are transplanted into their vicinity. Although this transcriptional silencing has been widely characterized using reporter genes, the ability of telomeres to repress natural subtelomeric genes has remained uncertain. In a previous report we described telomeric silencing of a yeast retrotransposon.