CiteULike: di gandrian library [10 articles]

The transcriptional regulator SsuR activates expression of the Corynebacterium glutamicum sulphonate utilization genes in the absence of sulphate

Daniel Koch — 2005-10-01T14:05:58-00:00

Molecular Microbiology, Vol. 58, No. 2. (October 2005), pp. 480-494.

RNaseE and RNA Helicase B Play Central Roles in the Cytoskeletal Organization of the RNA Degradosome.

A Taghbalout — 2008-05-26T11:33:04-00:00

The Journal of biological chemistry, Vol. 283, No. 20. (16 May 2008), pp. 13850-13855.

The RNA degradosome of Escherichia coli is a multiprotein complex that plays an essential role in normal RNA processing and decay. It was recently shown that the major degradosome constituents are organized in a coiled cytoskeletal-like structure that extends along the length of the cell. Here we show that the endoribonuclease E (RNaseE) and RNA helicase B (RhlB) components of the degradosome can each independently form coiled structures in the absence of the other degradosome proteins. In contrast, the cytoskeletal organization of the other degradosome proteins required the presence of the RNaseE or RhlB coiled elements. Although the RNaseE and RhlB structures were equally competent to support the helical organization of polynucleotide phosphorylase, the cytoskeletal-like organization of enolase occurred only in the presence of the RNaseE coiled structure. The results indicate that the RNA degradosome proteins are components of the bacterial cytoskeleton rather than existing as randomly distributed multiprotein complexes within the cell and suggest a model for the cellular organization of the components within the helical degradosomal structure.

Characterization of two thermostable cyanobacterial phytochromes reveals global movements in the chromophore-binding domain during photoconversion.

Andrew T Ulijasz — 2008-05-17T15:30:13-00:00

The Journal of biological chemistry (14 May 2008)

Photointerconversion between the red light-absorbing Pr form and the far-red light-absorbing Pfr form is the central feature that allows members of the phytochrome (Phy) superfamily to act as reversible switches in light perception. Whereas the chromophore structure and surrounding binding pocket of Pr have been described, those for Pfr have remained enigmatic for various technical reasons. Here, we describe a novel pair of Phys from two thermophilic cyanobacteria, Synechococcus sp. OS-A and OS-B', that overcome several of these limitations. Like other cyanobacterial Phys, SyA-Cph1 and SyB-Cph1 covalently bind the bilin phycocyanobilin (PCB) via their cGMP phosphodiesterase/adenyl cyclase/FhlA (GAF) domains and then assume the photointerconvertible Pr and Pfr states with absorption maxima at 630 and 704 nm, respectively. However, they are naturally missing the N-terminal Per/Arndt/Sim domain common to others in the Phy superfamily. Importantly, truncations containing only the GAF domain are monomeric, photochromic, and remarkably thermostable. Resonance Raman and NMR spectroscopy show that all four pyrrole ring nitrogens of PCB are protonated both as Pr and following red light irradiation, indicating that the GAF domain by itself can complete the Pr to Pfr photocycle. 1H-15N two-dimensional NMR spectra of isotopically-labeled preparations of the SyB-Cph1 GAF domain revealed that a number of amino acids change their environment during photoconversion of Pr to Pfr, which can be reversed by subsequent photoconversion back to Pr. Through three-dimensional NMR spectroscopy before and after light photoexcitation, it should now be possible to define the movements of the chromophore and binding pocket during photoconversion. We also generated a series of strongly red fluorescent derivatives of SyB-Cph1, which based on their small size and thermostability may be useful as cell biological reporters.

Infection by the 'photosynthetic' phage S-PM2 induces increased synthesis of phycoerythrin in Synechococcus sp. WH7803.

J Shan — 2008-05-17T15:28:20-00:00

FEMS microbiology letters, Vol. 283, No. 2. (June 2008), pp. 154-161.

Phycoerythrin-containing Synechococcus strains are unicellular cyanobacteria that are of great ecological importance in the marine environment. These organisms are known to be susceptible to infection by cyanophages (viruses that infect cyanobacteria). The infection cycle takes several hours and during this time the cyanophages may potentially modify the cyanobacterial light-harvesting apparatus. This study based on a model system consisting of Synechococcus sp. WH7803 and cyanophage S-PM2 revealed a progressive increase in the content of phycoerythrin per cell and per phycobilisome postinfection using absorption and emission spectrophotometry and sodium dodecyl sulphate-polyacrylamide gel electrophoresis. An increased cellular content of chlorophyll a was also revealed using absorption spectrophotometry. The transcript levels of the phycoerythrin-coding operons, mpeBA and cpeBA, were found to increase after phage infection using quantitative real-time PCR. This phage-induced increase in light-harvesting capacity could potentially increase the photosynthetic activity of the host to satisfy the phage's energy demand for reproduction.

NblR is a novel one-component response regulator in the cyanobacterium Synechococcus elongatus PCC 7942.

H Kato — 2008-05-10T18:58:18-00:00

Bioscience, biotechnology, and biochemistry, Vol. 72, No. 4. (April 2008), pp. 1072-1079.

A response regulator, NblR, of the cyanobacterium Synechococcus elongatus PCC 7942 is known to induce expression of the nblA gene, a key factor in phycobilisome degradation (bleaching) under nutrient-deprivation conditions. In this study, we observed phosphorylation-independent regulation of NblR activity. We constructed a mutant strain expressing NblR (D57A), in which a putative phospho-accepting Asp-57 was replaced with Ala residue. Under nitrogen deprivation, this strain exhibited the typical bleaching phenotype observed in wild-type cells. Moreover, in the mutant, the nblA transcript accumulated at a level similar to that of the wild type. Our results indicate that activation of NblR is independent of phosphorylation, if any, by a cognate histidine kinase. Screening of proteins interacting with NblR by yeast two-hybrid analysis revealed two candidates, MreC and NarB, suggesting a novel mechanism that activates NblR, or other functions of the response regulator.

The regulatory factor SipA provides a link between NblS and NblR signal transduction pathways in the cyanobacterium Synechococcus sp. PCC 7942.

P Salinas — 2008-05-10T18:55:03-00:00

Molecular microbiology, Vol. 66, No. 6. (December 2007), pp. 1607-1619.

Cyanobacteria respond to environmental stress conditions by adjusting its photosynthesis machinery. When subjected to nutrient and high light stress, Synechococcus sp. PCC 7942 and other non-diazotrophic cyanobacteria degrade their phycobilisome, the light-harvesting complexes for photosynthesis. Phycobilisome degradation requires convergence of multiple signals onto the nblA gene. Despite considerable efforts to identify regulatory proteins involved in acclimation responses, the signal transduction mechanisms involved remain largely unknown. However, we show here that SipA, a protein that binds to the ATP-binding domain of the histidine kinase NblS, counteracts the function of the response regulator NblR in acclimation to stress, and is also involved in downregulation of the nblA gene. The integrity of the HLR1 element overlapping P(nblA-1) and P(nblA-2) promoters is required for downregulation of the nblA gene. Induction by NblR is strongly dependent on DNA sequences located at least 44 bp upstream transcription initiation from P(nblA-2), and is also hampered by point mutations at HLR1. Genetic evidence of the antagonistic roles of NblR and SipA at regulation of the nblA gene, chlorosis and survival from stress is presented.

Baeocytes in the cyanobacterium Pleurocapsa sp.: Characterization of the differentiated cells produced by multiple fission

A Pinevich — 2008-05-09T14:35:35-00:00

Microbiology, Vol. 77, No. 1. (20 February 2008), pp. 62-68.

Abstract Electron microscopy of cyanobacterium Pleurocapsa sp. CALU 1126 revealed that multiple fission proceeds by successive binary fissions. The cultivation conditions were determined when the number of baeocytes (products of multiple fission) was comparable with that of macrocytes (products of binary fission), and cell sorting was achieved for the first time. Juvenile baeocytes were shown to differ from macrocytes in: (1) the absence of sheath; (2) the linear-peripheral configuration of their lamellar system; (3) lower content of phycobiliproteins and higher content of carotenoids; (4) the set of PSII polypeptides. Baeocytes can therefore be considered differentiated cells characterized by the uncoupling between energy and biosynthetic metabolism.

Algae acquire vitamin B12 through a symbiotic relationship with bacteria

Martin Croft — 2005-11-03T02:12:30-00:00

Nature, Vol. 438, No. 7064., pp. 90-93.

Think big giant genes in bacteria

Reva — 2008-01-31T11:44:15-00:00

Environmental Microbiology, Vol. 10, No. 3. (March 2008), pp. 768-777.