Post-Transcriptional Control of Photosynthesis Gene Expression. In: Blankenship RE, Madigan MT, Bauer CE, editors. Anoxygenic Photosynthetic Bacteria. Dordrecht: Springer Netherlands; 1995. pp. 1235-44. [DOI: 10.1007/0-306-47954-0_59]

Characterization of a mutant strain of Rhodovulum sulfidophilum lacking the pufA and pufB genes encoding the polypeptides for the light-harvesting complex 1 (B 870)

Contradictory results on the effectiveness of energy transfer from the light harvesting complex 2 (LH2) directly to the reaction center (RC) in mutant strains lacking the core light-harvesting complex 1 (LH1) have been obtained with cells of Rhodobacter capsulatus and Rhodobacter sphaeroides. A LH1(-) mutant of Rhodovulum sulfidophilum, named rsLRI, was constructed by deletion of the pufBA genes, resulting in a kanamycin resistant photosynthetically positive clone. To restore the wild type phenotype, a complemented strain C2 was constructed by inserting in trans a DNA segment containing the pufBA genes. Light-induced FTIR difference spectra indicate that the RC in the rsLRI mutant and in the C2 complemented strains are functionally and structurally identical with those in the wild type strain, demonstrating that the assembly and the function of the RC is not impaired by the LH1 deletion. The photosynthetic growth rate of the rsLRI strain increased with decreasing light intensity. At 50 W m(-2 )no photosynthetic growth was observed. These results indicate that the light energy harvested by the LH2 complex was not or inefficiently transferred to the RC; thus most of the energy necessary for photosynthetic growth is in the LH1(-) strain directly absorbed by the RC. It is supposed that in the mutant strain, RC and LH2 cannot interact in an efficient way.

Transcriptional control of expression of genes for photosynthetic reaction center and light-harvesting proteins in the purple bacterium Rhodovulum sulfidophilum

The purple photosynthetic bacterium Rhodovulum sulfidophilum synthesizes photosynthetic apparatus even under highly aerated conditions in the dark. To understand the oxygen-independent expression of photosynthetic genes, the expression of the puf operon coding for the light-harvesting 1 and reaction center proteins was analyzed. Northern blot hybridization analysis showed that puf mRNA synthesis was not significantly repressed by oxygen in this bacterium. High-resolution 5' mapping of the puf mRNA transcriptional initiation sites and DNA sequence analysis of the puf upstream regulatory region indicated that there are three possible promoters for the puf operon expression, two of which have a high degree of sequence similarity with those of Rhodobacter capsulatus, which shows a high level of oxygen repression of photosystem synthesis. Deletion analysis showed that the third promoter is oxygen independent, but the activity of this promoter was not enough to explain the aerobic level of mRNA. The posttranscriptional puf mRNA degradation is not significantly influenced by oxygen in R. sulfidophilum. From these results, we conclude that puf operon expression in R. sulfidophilum is weakly repressed by oxygen, perhaps as a result of the following: (i) there are three promoters for puf operon transcription, at least one of which is oxygen independent; (ii) readthrough transcripts which may not be affected by oxygen may be significant in maintaining the puf mRNA levels; and (iii) the puf mRNA is fairly stable even under aerobic conditions.

Expression of P(II) and glutamine synthetase is regulated by P(II), the ntrBC products, and processing of the glnBA mRNA in Rhodospirillum rubrum

We have studied the transcription of the glnB and glnA genes in Rhodospirillum rubrum with firefly luciferase as a reporter enzyme. Under NH(4)(+) and N(2) conditions, glnBA was cotranscribed from a weak and a strong promoter. In nitrogen-fixing cultures, activity of the latter was highly enhanced by NtrC, but transcription from both promoters occurred under both conditions. There is no promoter controlling transcription of glnA alone, supporting our proposal that the glnA mRNA is produced by processing.

Transcript cleavage, attenuation, and an internal promoter in the Rhodobacter capsulatus puc operon

The stoichiometry of the structural proteins of the photosynthetic apparatus in purple photosynthetic bacteria is achieved primarily by complex regulation of the levels of mRNA encoding the different proteins, which has been studied in the greatest detail in the puf operon. Here we investigated the transcriptional and posttranscriptional regulation of the puc operon, which encodes the peripheral light harvesting complex LHII. We show that, analogous to the puf operon, a primary transcript encoding five puc genes is rapidly processed to generate more stable RNA subspecies. Contrary to previous hypotheses, translational coupling and regulation of puc transcription by puc gene products were found not to occur. A putative RNA stem-loop structure appears to attenuate transcription initiated at the puc operon major promoter. We also found that a minor pucD-internal promoter contributes to the levels of a message that encodes the LHII 14-kDa gamma (PucE) protein.

Analysis of the puc operon promoter from Rhodobacter capsulatus

Expression of the Rhodobacter capsulatus puc operon, which codes for structural polypeptides of the light-harvesting-II peripheral antenna complex, is highly regulated in response to alterations in oxygen tension and light intensity. To obtain an understanding of the puc promoter region we report the high-resolution 5' mapping of the puc mRNA transcriptional start site and DNA sequence analysis of the puc upstream regulatory sequence (pucURS). A sigma70-type promoter sequence was identified (pucP1) which has a high degree of sequence similarity with carotenoid and bacteriochlorophyll biosynthesis promoters. Inspection of the DNA sequence also indicated the presence of two CrtJ and four integration host factor (IHF) binding sites. Transcriptional fusions of the pucURS fused to lacZ also confirmed that puc promoter activity is regulated by the transcriptional regulators IHF, CrtJ, and RegA. Gel retardation analysis using cell extracts indicates that mutations in IHF and RegA disrupt protein binding to DNA fragments containing the pucURS.

Structure of the puf operon of the obligately aerobic, bacteriochlorophyll alpha-containing bacterium Roseobacter denitrificans OCh114 and its expression in a Rhodobacter capsulatus puf puc deletion mutant

Roseobacter denitrificans (Erythrobacter species strain OCh114) synthesizes bacteriochlorophyll a (BChl) and the photosynthetic apparatus only in the presence of oxygen and is unable to carry out primary photosynthetic reactions and to grow photosynthetically under anoxic conditions. The puf operon of R. denitrificans has the same five genes in the same order as in many photosynthetic bacteria, i.e., pufBALMC. PufC, the tetraheme subunit of the reaction center (RC), consists of 352 amino acids (Mr, 39,043); 20 and 34% of the total amino acids are identical to those of PufC of Chloroflexus aurantiacus and Rubrivivax gelatinosus, respectively. The N-terminal hydrophobic domain is probably responsible for anchoring the subunit in the membrane. Four heme-binding domains are homologous to those of PufC in several purple bacteria. Sequences similar to pufQ and pufX of Rhodobacter capsulatus were not detected on the chromosome of R. denitrificans. The puf operon of R. denitrificans was expressed in trans in Escherichia coli, and all gene products were synthesized. The Roseobacter puf operon was also expressed in R. capsulatus CK11, a puf puc double-deletion mutant. For the first time, an RC/light-harvesting complex I core complex was heterologously synthesized. The strongest expression of the R. denitrificans puf operon was observed under the control of the R. capsulatus puf promoter, in the presence of pufQ and pufX and in the absence of pufC. Charge recombination between the primary donor P+ and the primary ubiquinone Q(A)- was observed in the transconjugant, showing that the M and L subunits of the RC were correctly assembled. The transconjugants did not grow photosynthetically under anoxic conditions.

Gene cloning and regulation of gene expression of the puc operon from Rhodovulum sulfidophilum

Rhodovulum (Rhv.) sulfidophilum, unlike other nonsulfur purple bacteria, is able to synthesize the peripheral antenna complex even under fully aerobic conditions in the dark. We have obtained strong evidence that Rhv. sulfidophilum encodes only one copy of the puc operon, comprising pucB, pucA and pucC. pucB and pucA encode the beta- and alpha-polypeptides. The third ORF (pucC), downstream of pucA, has a strong homology to pucC of Rhodobacter (Rb.) capsulatus. Deletion mutation analysis indicated that the requirement for the pucC gene product for LH II expression was less strict than in Rb. capsulatus. Comparison of the deduced alpha and beta polypeptide sequences with the directly determined primary structure revealed a C-terminal processing of the alpha-subunit. Primer extension analysis showed that the pucBAC is transcribed from a sigma70-type promoter 130 bases upstream of the translational start of pucB. Transcriptional expression of the pucBAC operon in Rhv. sulfidophilum is higher, the lower the light intensity is, and is not reduced to a ground-level by the presence of oxygen. Based on lacZ fusions the relative promoter activities were, for dark aerobic:dark semiaerobic:low light anaerobic:medium light anaerobic:high light anaerobic, 5.5:7.0:2.0:1.0:0.78. Still unidentified cis-regulatory elements or binding sites of trans-regulatory elements are apparently localized in two distinct upstream regions. Furthermore, comparison of the promoter region of the Rhv. sulfidophilum pucBAC with the promoter regions of puc operons in related species showed distinct differences in the regulatory elements. The significance of these results with respect to the regulation of transcription and the oxygen-independent synthesis of LH II from Rhv. sulfidophilum is discussed.

Forty-five years of developmental biology of photosynthetic bacteria

Developmental biology and cell differentiation of photosynthetic prokaryotes are less noticed fields than the showpieces of eukaryotes, e.g. Drosophila melanogaster. The large metabolic versatility of the facultative purple bacteria and their great capability to adapt to different ecological conditions, however, aroused the inquisitiveness to investigate the process of cell differentiation and to use these bacteria as model system to study structure, function and biosynthesis of the photosynthetic apparatus. The great progress in research in this field paved the way to study principal mechanisms of cellular organization and differentiation in these bacteria. In this article, the history of the research on membrane structure and development of anoxygenic photosynthetic prokaryotes during the last 45 years is described. A personal account of how I entered the field through research on the phototaxis of cyanobacteria is given. Intracytoplasmic membranes (ICM) were detected by electron microscopy in cyanobacteria and in purple non-sulfur bacteria. The formation of ICM by invagination of the cytoplasmic membrane in purple bacteria was observed for the first time. Investigations on the effect of changes in oxygen tension and light intensity on the formation of pigments and intracytoplasmic membranes followed. The isolation, purification, and analysis of light-harvesting complexes and of pigment-binding proteins was the next step of our research. Lipopolysaccharides and peptidoglycans were detected and analyzed in the outer membrane of photosynthetic bacteria. Functional membrane differentiation includes variations in the rates of photophosphorylation and electron transport. Molecular genetic approaches have initiated the investigation of transcriptional regulation and the analysis of correlation between pigment and protein synthesis. Molecular analysis of assembly of light-harvesting complexes and membrane differentiation are the present aspects of our research. Cell differentiation has been considered under evolutionary view.