Post-transcriptional Level In Response Research Articles

CpxR/OmpR interplay regulates curli gene expression in response to osmolarity in Escherichia coli.

Curli fibers could be described as a virulence factor able to confer adherence properties to both abiotic and eukaryotic surfaces. The ability to adapt rapidly to changing environmental conditions through signal transduction pathways is crucial for the growth and pathogenicity of bacteria. OmpR was shown to activate csgD expression, resulting in curli production. The CpxR regulator was shown to negatively affect curli gene expression when binding to its recognition site that overlaps the csgD OmpR-binding site. This study was undertaken to clarify how the interplay between the two regulatory proteins, OmpR and CpxR, can affect the transcription of the curli gene in response to variation of the medium osmolarity. Band-shift assays with purified CpxR proteins indicate that CpxR binds to the csgD promoter region at multiple sites that are ideally positioned to explain the csg repression activity of CpxR. To understand the physiological meaning of this in vitro molecular phenomenon, we analyzed the effects of an osmolarity shift on the two-component pathway CpxA/CpxR. We establish here that the Cpx pathway is activated at both transcriptional and posttranscriptional levels in response to a high osmolarity medium and that CpxR represses csgD expression in high-salt-content medium, resulting in low curli production. However, csgD repression in response to high sucrose content is not mediated by CpxR but by the global regulatory protein H-NS. Therefore, multiple systems (EnvZ/OmpR, Cpx, Rcs, and H-NS) appear to be involved in sensing environmental osmolarity, leading to sophisticated regulation of the curli genes.

Multiple Regulatory Mechanisms Maintain Zinc Homeostasis in Saccharomyces cerevisiae

Zinc is an essential nutrient, yet it is toxic if it accumulates in excess amounts within cells; therefore the intracellular labile zinc content of cells is tightly controlled. In Saccharomyces cerevisiae, zinc homeostasis is regulated by the controlled activity of zinc uptake transporters in the plasma membrane and transporters responsible for intracellular zinc compartmentalization. The activity of these transporters is regulated at both transcriptional and posttranscriptional levels in response to zinc. These different mechanisms work together to precisely balance zinc uptake and its storage and utilization.

The role of sigma factors in plastid transcription

Expression of plastid genes is controlled at both transcriptional and post-transcriptional levels in response to developmental and environmental signals. In many cases this regulation is mediated by nuclear-encoded proteins acting in concert with the endogenous plastid gene expression machinery. Transcription in plastids is accomplished by two distinct RNA polymerase enzymes, one of which resembles eubacterial RNA polymerases in both subunit structure and promoter recognition properties. The holoenzyme contains a catalytic core composed of plastid-encoded subunits, assembled with a nuclear-encoded promoter-specificity factor, sigma. Based on examples of transcriptional regulation in bacteria, it is proposed that differential activation of sigma factors may provide the nucleus with a mechanism to control expression of groups of plastid genes. Hence, much effort has focused on identifying and characterizing sigma-like factors in plants. While fractionation studies had identified several candidate sigma factors in purified RNA polymerase preparations, it was only 4 years ago that the first sigma factor genes were cloned from two photosynthetic eukaryotes, both of which were red algae. More recently this achievement has extended to the identification of families of sigma-like factor genes from several species of vascular plants. Now, efforts in the field are directed at understanding the roles in plastid transcription of each member of the rapidly expanding plant sigma factor gene family. Recent results suggest that accumulation of individual sigma-like factors is controlled by light, by plastid type and/or by a particular stage of chloroplast development. These data mesh nicely with accumulating evidence that the core sigma-binding regions of plastid promoters mediate regulated transcription in response to light-regime and plastid type or developmental state. In this review I will outline progress made to date in identifying and characterizing the sigma-like factors of plants, and in dissecting their potential roles in chloroplast gene expression.

Dictyostelium ribosomal protein genes and the elongation factor 1B gene show coordinate developmental regulation which is under post-transcriptional control

Starvation for amino acids initiates the developmental program in the cellular slime mold, Dictyostelium discoideum [19, 20]. One of the earliest developmental events is the decline in ribosomal protein synthesis [2, 17, 29, 30]. The ribosomal protein mRNAs are excluded from polysomes with 20 min to 1 h following the removal of nutrients, and their mRNA levels decline sharply at about 9 h into the 24-h developmental cycle [28, 31, 35, 36]. It has been generally assumed that the decline in r-protein mRNA levels during late development reflected a decline in the transcription rate [12, 32, 43]. Here we demonstrate that this is not the case. The transcription rates of three ribosomal protein genes, rpL11, rpL23 and rpS9 as well as an elongation factor 1B gene have been determined during growth and development in Dictyostelium. Throughout growth and develoment the transcription rate of the ribosomal protein genes remains relatively constant at 0.2%–0.5% of the rate of rRNA transcription while the elongation factor 1B gene is transcribed at 0.4%–0.6% of the rRNA rate. This low but constant transcription rate is in contrast to a spore coat protein gene Psp D, which is transcribed at 6% of the rRNA rate in late developing cells. The elongation factor 1B gene appears to be co-regulated with the ribosomal protein genes both in terms of its transcription rate and mRNA accumulation. Dictyostelium has been a popular model for understanding signal transduction and the growth to differentiation transition, thus it is of significance that the regulation of ribosome biosynthesis in Dictyostelium resembles that of higher eukaryotes in being regulated largely at the post-transcriptional level in response to starvation as opposed to yeasts where the regulation is largely transcriptional [27].

Tissue Factor mRNA in THP-1 Monocytic Cells Is Regulated at Both Transcriptional and Posttranscriptional Levels in Response to Lipopolysaccharide †

Tissue factor (TF) is transiently expressed in human monocytes exposed to the inflammatory agonist bacterial lipopolysaccharide (LPS). Since TF is the major cellular initiator of the coagulation protease cascades, it is inferred that its expression within the vasculature is strictly regulated. In this study, we investigated mechanisms which control TF mRNA expression in the human monocytic cell line THP-1. LPS induced a rapid and transient accumulation of the mature 2.2-kb TF mRNA, which was maximal at 2 h. After stimulation, the rate of transcription of the TF gene was increased (3.3 +/- 1.3)fold. In addition, we observed a significant change in TF mRNA stability: at 1 h after LPS stimulation, TF mRNA was stable during a 60-min period and had a half-life of greater than 120 min, whereas at 2 h, the half-life had declined to 25 +/- 5 min. Furthermore, a larger (3.4-kb) TF RNA species was induced in these cells; the size of this species and data from selective hybridizations with intron-specific probes are consistent with the presence of an unspliced copy of intron 1. These results demonstrate that the LPS-induced accumulation of TF mRNA levels in these monocytic cells is accomplished by both transcriptional and posttranscriptional control mechanisms.

Tissue factor mRNA in THP-1 monocytic cells is regulated at both transcriptional and posttranscriptional levels in response to lipopolysaccharide.

Tissue factor (TF) is transiently expressed in human monocytes exposed to the inflammatory agonist bacterial lipopolysaccharide (LPS). Since TF is the major cellular initiator of the coagulation protease cascades, it is inferred that its expression within the vasculature is strictly regulated. In this study, we investigated mechanisms which control TF mRNA expression in the human monocytic cell line THP-1. LPS induced a rapid and transient accumulation of the mature 2.2-kb TF mRNA, which was maximal at 2 h. After stimulation, the rate of transcription of the TF gene was increased (3.3 +/- 1.3)fold. In addition, we observed a significant change in TF mRNA stability: at 1 h after LPS stimulation, TF mRNA was stable during a 60-min period and had a half-life of greater than 120 min, whereas at 2 h, the half-life had declined to 25 +/- 5 min. Furthermore, a larger (3.4-kb) TF RNA species was induced in these cells; the size of this species and data from selective hybridizations with intron-specific probes are consistent with the presence of an unspliced copy of intron 1. These results demonstrate that the LPS-induced accumulation of TF mRNA levels in these monocytic cells is accomplished by both transcriptional and posttranscriptional control mechanisms.