Molecular responses of Campylobacter jejuni to cadmium stress

Cadmium ions are a potent carcinogen in animals, and cadmium is a toxic metal of significant environmental importance for humans. Response curves were used to investigate the effects of cadmium chloride on the growth of Camplyobacter jejuni. In vitro, the bacterium showed reduced growth in the presence of 0.1 mm cadmium chloride, and the metal ions were lethal at 1 mm concentration. Two-dimensional gel electrophoresis combined with tandem mass spectrometry analysis enabled identification of 67 proteins differentially expressed in cells grown without and with 0.1 mm cadmium chloride. Cellular processes and pathways regulated under cadmium stress included fatty acid biosynthesis, protein biosynthesis, chemotaxis and mobility, the tricarboxylic acid cycle, protein modification, redox processes and the heat-shock response. Disulfide reductases and their substrates play many roles in cellular processes, including protection against reactive oxygen species and detoxification of xenobiotics, such as cadmium. The effects of cadmium on thioredoxin reductase and disulfide reductases using glutathione as a substrate were studied in bacterial lysates by spectrophotometry and nuclear magnetic resonance spectroscopy, respectively. The presence of 0.1 mm cadmium ions modulated the activities of both enzymes. The interactions of cadmium ions with oxidized glutathione and reduced glutathione were investigated using nuclear magnetic resonance spectroscopy. The data suggested that, unlike other organisms, C. jejuni downregulates thioredoxin reductase and upregulates other disulfide reductases involved in metal detoxification in the presence of cadmium.     

Cellular responses to replication stress: Implications in cancer biology and therapy

DNA replication is essential for cell proliferation. Any obstacles during replication cause replication stress, which may lead to genomic instability and cancer formation. In this review, we summarize the physiological DNA replication process and the normal cellular response to replication stress. We also outline specialized therapies in clinical trials based on current knowledge and future perspectives in the field.     

RNA silencing: Mechanism, biology and responses to environmental stress

Much early work on environmental stress, including ionizing radiation and environmental toxins, emphasised their action on DNA and subsequent mutagenesis in long term effects including germ cell mutagenesis, carcinogenesis and trans-generational effect. However, recent studies are increasingly pointing a complementary role of epigenetic effects in these processes. While a substantial part of the literature focuses on DNA methylation, there is increasing recognition of the role of non-coding RNAs, including small-, micro-, and pi-RNAs, as well as transposable elements. These play key roles in carcinogenesis, and in germ cell changes including trans-generational effects.     

Signaling pathways for stress responses and adaptation in Aspergillus species: stress biology in the post-genomic era

Aspergillus species are among the most important filamentous fungi in terms of industrial use and because of their pathogenic or toxin-producing features. The genomes of several Aspergillus species have become publicly available in this decade, and genomic analyses have contributed to an integrated understanding of fungal biology. Stress responses and adaptation mechanisms have been intensively investigated using the accessible genome infrastructure. Mitogen-activated protein kinase (MAPK) cascades have been highlighted as being fundamentally important in fungal adaptation to a wide range of stress conditions. Reverse genetics analyses have uncovered the roles of MAPK pathways in osmotic stress, cell wall stress, development, secondary metabolite production, and conidia stress resistance. This review summarizes the current knowledge on the stress biology of Aspergillus species, illuminating what we have learned from the genomic data in this “post-genomic era.”     

Molecular biology in physiology

The aim of this symposium on molecular biology in physiology was to introduce molecular biology to physiologists who had relatively little exposure to the new developments in this field, so that they can become conversant on this topic and contribute to the advancement of physiology by incorporating molecular biological approaches as a part of their research arsenal. After the discussion of the basic concepts, terminology, and methodology used in molecular biology, it was shown how these basic principles have been applied to the study of the genes encoding two membrane proteins that have important transport functions (band 3 and ATPase). The second half of the symposium consisted of papers on the state-of-the-art developments in the application of molecular biology to the studies of the atrial natriuretic factor and renin genes, adenylate cyclase-coupled adrenergic receptors, acetylcholine receptors and sodium channel, and long-term and short-term memories. The ultimate goal is that these examples will provide an impetus for the opening of new frontiers of research in physiology by taking advantage of the tools developed from recent advances in molecular biology.     

Molecular biology in biorheology

This presentation is aimed at giving some background information on molecular biology, thus serving as an introduction to the Symposium on Molecular Biorheology held during the Sixth International Congress of Biorheology in Vancouver. The papers presented at this Symposium indicate that the use of molecular biological techniques allows the understanding of normal and abnormal rheological properties of cells and organs at the molecular level. It is hoped that these examples will provide an impetus for us to open new frontiers of research in biorheology by taking advantage of the powerful tools developed from recent advances in molecular biology.     

Molecular and genetic aspects of plant responses to osmotic stress

Drought, high salinity and freezing impose osmotic stress on plants. Plants respond to the stress in part by modulating gene expression, which eventually leads to the restoration of cellular homeostasis, detoxification of toxins and recovery of growth. The signal transduction pathways mediating these adaptations can be dissected by combining forward and reverse genetic approaches with molecular, biochemical and physiological studies. Arabidopsis is a useful genetic model system for this purpose and its relatives including the halophyte Thellungiella halophila, can serve as valuable complementary genetic model systems.     

Molecular biology of herbicides

One of the most dynamic areas of plant molecular biology is the investigation of the actions of three classes of herbicides: s-triazines (atrazine, simazine), glyphosate, and sulfonylureas (chlorsulfuron, sulfometuron methyl) (Figure 1). The results of this work are expected to provide the first significant applications of plant biotechnology: directly, in the genetic engineering of crop plants resistant to specific herbicides and, indirectly, in providing a molecular basis for the rational design of new herbicides for specific biological targets. s-Triazines affect photosynthesis by inhibiting the binding of quinones to the chloroplast membrane Q_B protein. An s-triazine resistant Q_B protein isolated from weeds in fields consistently treated with the herbicide has a serine in place of a glycine in this highly conserved protein. Glyphosate inhibits 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSP synthase), an enzyme in the aromatic amino acid biosynthetic pathway. Mutagenized bacteria produce a resistant EPSP synthase with a substitution of serine for proline. Sulfonylureas inhibit the acetolactate synthase (ALS) of bacteria, yeast, and higher plants; this enzyme catalyzes the first step in the synthesis of branched chain amino acids. Resistant ALS has been found in bacteria, yeast and tobacco with a proline substituted by serine in yeast ALS. These findings provide a strong basis for developing projected plant biotechnology applications.     

Molecular biology of complement

Complementary DNA clones corresponding to most of the proteins of a major amplification and effector of immune host defenses, the complement system, have been isolated and characterized. Availability of these molecular probes has substantially increased our information about and understanding of the structure of the complement proteins and regulation of complement gene expression. Information about the proteins has led to the generation of potential pharmacological agents for the selective control of inflammation. Understanding of the regulatory mechanism has provided insights into the mechanisms accounting for the response to several cytokines including interferon-gamma, interleukin-1 and tumor necrosis factor. Finally, complement molecular genetics has been stimulated so that the basis for several complement deficiency disorders has been elucidated.     

Molecular biology of proteasomes

Eukaryotic proteasomes are unusually large proteins with a heterogeneous subunit composition and have been classified into two isoforms with apparently distinct sedimentation coefficients of 20S and 26S. The 20S proteasome is composed of a set of small subunits with molecular masses of 21–32 kDa. The 26S proteasome is a multi-molecular assembly, consisting of a central 20S proteasome and two terminal subsets of multiple subunits of 28–112 kDa attached to the central part in opposite orientations. The primary structures of all the subunits of mammalian and yeast 20S proteasomes have been deduced from the nucleotide sequences of cDNAs or genes isolated by recombinant DNA techniques. These genes constitute a unique multi-gene family encoding homologous polypeptides that have been conserved during evolution. In contrast, little is yet known about the terminal structures of the 26S proteasome, but the cDNA clonings of those of humans are currently in progress. In this review, I summarize available information of the structural features on eukaryotic 20S and 26S proteasomes which has been clarified by molecular-biological methods.     

Molecular biology of archaebacteria

In the process of phylogenetic studies, based on the comparative analysis of sequences of 16S (18S) rRNA, C. Woese and collaborators discovered that some microorganisms, which previously had been described as bacteria, form a group named archaebacteria, differing from other bacteria as well as from eukaryotes to the same extent as the latter differ from each other. A review of the work leading to that result, as well as characteristics of archaebacteria with emphasis on their biochemistry and molecular biology, is presented.