CiteULike: llchristensen's library [8 articles]

Selection of housekeeping genes for gene expression studies in human reticulocytes using real-time PCR

Nicholas Silver — 2006-10-07T00:28:37-00:00

BMC Molecular Biology, Vol. 7 (06 October 2006), 33.

UVB Effects on the Photosystem II-D1 Protein of Phytoplankton and Natural Phytoplankton Communities

Josee Bouchard — 2008-04-09T22:44:11-00:00

Photochemistry and Photobiology, Vol. 82, No. 4. (2006), pp. 936-951.

ABSTRACT The reaction center of photosystem II is susceptible to photodamage. In particular the D1 protein located in the photosystem II core has a rapid, light-dependent turnover termed the photosystem II repair cycle that, under illumination, degrades and resynthesizes D1 protein to limit accumulation of photodamaged photosystem II. Most studies concerning the effects of UVB (280-320 nm) on this cycle have been on cyanobacteria or specific phytoplankton species rather than on natural communities of phytoplankton. During a 5-year multidisciplinary project on the effects of UV radiation (200-400 nm) on natural systems, the effects of UVB on the D1 protein of natural phytoplankton communities were assessed. This review provides an overview of photo-inhibitory effects of light on cultured and natural phytoplankton, with an emphasis on the interrelation of UVB exposure, D1 protein degradation and the repair of photosystem II through D1 resynthesis. Although the UVB component of the solar spectrum contributes to the primary photoinactivation of photosystem II, we conclude that, in natural communities, inhibition of the rate of the photosystem II repair cycle is a more important influence of UVB on primary productivity. Indeed, exposing tropical and temperate phytoplankton communities to supplemented UVB had more inhibitory effect on D1 synthesis than on the D1 degradation process itself. However, the rate of net D1 damage was faster for the tropical communities, likely because of the effects of high ambient light and water temperature on mechanisms of protein degradation and synthesis.

Ultraviolet-B photodestruction of a light-harvesting complex

Kaiqin Lao — 2008-04-09T16:47:11-00:00

Proceedings of the National Academy of Sciences, Vol. 93, No. 11. (28 May 1996), pp. 5258-5263.

10.1073/pnas.93.11.5258

Electron transfer in ruthenium-modified proteins

Morten Bjerrum — 2008-03-27T14:33:09-00:00

Journal of Bioenergetics and Biomembranes, Vol. 27, No. 3. (1 June 1995), pp. 295-302.

Photochemical techniques have been used to measure the kinetics of intramolecular electron transfer in Ru(bpy)2(im)(His)2+-modified (bpy = 2,2′-bipyridine; im = imidazole) cytochromec and azurin. A driving-force study with the His33 derivatives of cytochromec indicates that the reorganization energy (γ) for Fe2+→Ru3+ ET reactions is 0.8 eV. Reductions of the ferriheme by either an excited complex,*Ru2+, or a reduced complex, Ru+, are anomalously fast and may involve formation of an electronically excited ferroheme. The distance dependence of Fe2+→Ru3+ and Cu+→Ru3+ electron transfer in 12 different Ru-modified cytochromes and azurins has been analyzed using a tunneling-pathway model. The ET rates in 10 of the 12 systems exhibit an exponential dependence on metal-metal separation (decay constant of 1.06 å−1) that is consistent with predictions of the pathway model.

Adaptation to high light intensity in Synechococcus sp. strain PCC 7942: regulation of three psbA genes and two forms of the D1 protein.

RD Kulkarni — 2008-03-24T21:29:55-00:00

J Bacteriol, Vol. 176, No. 4. (February 1994), pp. 959-965.

The three psbA genes in the cyanobacterium Synechococcus sp. strain PCC 7942 encode two distinct forms of the D1 protein of photosystem II. The psbAI message, which encodes form I, dominates the psbA transcript pool at low to moderate light intensities; however, exposure to high light triggers a response in which the psbAI message is actively degraded while psbAII and psbAIII, which encode form II, are transcriptionally induced. We addressed whether these changes result from a generalized stress response and examined the consequence of light-responsive psbA regulation on the composition of D1 in thylakoid membranes. Heat shock and oxidative stress had some effect on levels of the three psbA transcripts but did not produce the responses generated by an increase in light intensity. Prolonged exposure to high light (24-h time course) was characterized by elevated levels of all psbA transcripts through maintenance of high levels of psbAII and psbAIII messages and a rebound of the psbAI transcript after its initial decline. Form II-encoding transcripts were enriched relative to those encoding form I at all high-light time points. Form II replaced form I in the thylakoid membrane at high light despite an abundance of psbAI transcript at later time points; this may be explained by the observed faster turnover of form I than form II in the membrane. We propose that form II is less susceptible to damage at high light and that this qualitative alteration, coupled with increased turnover of D1, protects the cells from photoinhibition.

Dynamics of Fluxes Through Photosynthetic Complexes in Response to Changing Light and Inorganic Carbon Acclimation in Synechococcus elongatus

Tyler Mackenzie — 2005-09-21T12:26:38-00:00

Photosynthesis Research, Vol. 85, No. 3. (September 2005), pp. 341-357.

Characterization of a four-member psbA gene family from the cyanobacterium Anabaena PCC 7120

Jacqueline Vrba — 2008-03-24T21:16:38-00:00

Plant Molecular Biology, Vol. 14, No. 1. (1 January 1990), pp. 81-92.

The cyanobacterium Anabaena PCC 7120 contains a multigene family that encodes the D1 polypeptide of Photosystem II. This family consists of four members denoted psbAI-IV that are each unique but highly homologous. psbAII, III and IV are more closely related to each other than to psbAI. These three copies encode identical polypeptides that differ from the psbAI product by 21 amino acids. The transcription initiation site for psbAI has been mapped to 64–65 nucleotides upstream from the coding region. Primer extension assays performed with an oligonucleotide specific for psbAII, III and IV transcripts suggest that one or more of these genes is also expressed. Genomic mapping and chromosome walking experiments demonstrate that none of the four psbA copies is within 20 kbp of another member of the gene family.

Cyanobacterial psbA families in Anabaena and Synechocystis encode trace, constitutive and UVB-induced D1 isoforms

Cosmin Sicora — 2008-03-24T21:13:44-00:00

Biochimica et Biophysica Acta (BBA) - Bioenergetics, Vol. 1757, No. 1. (January 2006), pp. 47-56.

Cyanobacteria cope with UVB induced photoinhibition of Photosystem II by regulating multiple psbA genes to boost the expression of D1 protein (in Synechocystis sp. PCC6803), or to exchange the constitutive D1:1 protein to an alternate D1:2 isoform (in Synechococcus sp. PCC7942). To define more general patterns of cyanobacterial psbA expression, we applied moderately photoinhibitory UVB to Anabaena sp. PCC7120 and tracked the expression of its five psbA genes. psbAI, encoding a D1:1 protein isoform characterized by a Gln130, represented the majority of the psbA transcript pool under control conditions. psbAI transcripts decreased upon UVB treatment but the total psbA transcript pool increased 3.5 fold within 90 min as a result of sharply increased psbAII, psbAIV and psbAIII transcripts encoding an alternate D1:2 protein isoform characterized by Glu130, similar to that of Synechococcus. Upon UVB treatment the relaxation of flash induced chlorophyll fluorescence showed a characteristic acceleration of a decay phase likely associated with the exchange from the D1:1 protein isoform encoded by psbAI to the alternate D1:2 isoform encoded by psbAIV, psbAII and psbAIII. Throughout the UVB treatment the divergent psbA0 made only a trace contribution to the total psbA transcript pool. This suggests a similarity to the divergent psbAI gene from Synechocystis, whose natural expression we demonstrate for the first time at a trace level similar to psbA0 in Anabaena. These trace-expressed psbA genes in two different cyanobacteria raise questions concerning the functions of these divergent genes.