Combination of cyclohexane and piperazine based κ-opioid receptor agonists: Synthesis and pharmacological evaluation of trans,trans-configured perhydroquinoxalines

Desymmetrization of the pseudochiral (2r)-configured cyclohexane-1,2,3-triamines 8 with dimethyl oxalate led to racemic aminoquinoxaline-2,3-diones 9. Selective introduction of the κ pharmacophoric structural elements pyrrolidine and 3,4-dichlorophenylacetamide with a two-carbon distance afforded conformationally restricted κ agonists 13–15 based on the quinoxaline ring system. In competitive radioligand receptor binding studies the benzylamine 13b, the secondary amine 14b, and the carbamate 15 displayed high κ receptor affinity. The K_i value of the lead compound derived methoxycarbonyl derivative 15 is 9.7 nM. However, the κ affinity of 15 is exceeded by 13b and 14b with a basic functional group instead of the methoxycarbonyl group in 1-position of the quinoxaline system. The chlorine atoms of the dichlorophenylacetyl residue are essential, since the corresponding phenylacetyl analogs show considerably reduced κ affinity. The potent κ ligands 13b, 14b and 15 are selective over the related μ- and δ-opioid receptors, σ₁, σ₂ and NMDA receptors. In the [³⁵S]GTPγS-binding assay 13b behaved as partial agonist with lower activity than U-69,593.     

Nitrogen Oxyanion-dependent Dissociation of a Two-component Complex That Regulates Bacterial Nitrate Assimilation

Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression.     

Dual Binding Mode of the Nascent Polypeptide-associated Complex Reveals a Novel Universal Adapter Site on the Ribosome

Nascent polypeptide-associated complex (NAC) was identified in eukaryotes as the first cytosolic factor that contacts the nascent polypeptide chain emerging from the ribosome. NAC is present as a homodimer in archaea and as a highly conserved heterodimer in eukaryotes. Mutations in NAC cause severe embryonically lethal phenotypes in mice, Drosophila melanogaster, and Caenorhabditis elegans. In the yeast Saccharomyces cerevisiae NAC is quantitatively associated with ribosomes. Here we show that NAC contacts several ribosomal proteins. The N terminus of βNAC, however, specifically contacts near the tunnel exit ribosomal protein Rpl31, which is unique to eukaryotes and archaea. Moreover, the first 23 amino acids of βNAC are sufficient to direct an otherwise non-associated protein to the ribosome. In contrast, αNAC (Egd2p) contacts Rpl17, the direct neighbor of Rpl31 at the ribosomal tunnel exit site. Rpl31 was also recently identified as a contact site for the SRP receptor and the ribosome-associated complex. Furthermore, in Escherichia coli peptide deformylase (PDF) interacts with the corresponding surface area on the eubacterial ribosome. In addition to the previously identified universal adapter site represented by Rpl25/Rpl35, we therefore refer to Rpl31/Rpl17 as a novel universal docking site for ribosome-associated factors on the eukaryotic ribosome.     

Response of muscle-based biochemical condition indices to short-term variations in food availability in post-flexion reared sea bass Dicentrarchus labrax (L.) larvae

Six condition indices based on RNA, total soluble protein and two metabolic enzymes [lactate dehydrogenase (LDH) and citrate synthase (CS)] were analysed in muscle tissue of individual larvae, post-flexion reared sea bass Dicentrarchus labrax using DNA and total soluble protein as standards for size. In addition, the effect of 2 days of food deprivation on the cell proliferation rates was assessed. The RNA:DNA best reflected short-term changes in feeding conditions. If standardized by DNA content, LDH activity was a better indicator of condition than any other index but RNA:DNA. Further, the analysis of cell proliferation rates in muscle from 26 day-old larvae proved useful in distinguishing continuously fed larvae from individuals subjected to 2 days of fast.     

Structure and variation in ribosomal RNA genes of pea

Summary A complete ribosomal DNA (rDNA) repeat unit has been cloned from the genome of Pisum sativum (garden pea) and used to construct a map containing a total of 58 cleavage sites for 23 different restriction enzymes. Regions encoding 18s and 25s ribosomal RNA (rRNA) were identified by R-loop analysis. A 180 bp sequence element is repeated eight times in the intergenic nontranscribed spacer (NTS) region, as defined by eight evenly spaced RsaI cleavage sites. Sequence heterogeneity among these elements (subrepeats) is indicated by the presence of an NcoI site within the five RsaI subrepeats distal to the 25s rRNA gene but not in the three subrepeats proximal to this gene, and also by the presence of an additional RsaI cleavage site in one subrepeat.The approximately 4000 copies of the rDNA repeat in the pea nuclear genome show considerable heterogeneity with respect to the length of the NTS region, and differences are also frequently observed between different genotypes. In both cases the length variation appears to be due primarily to differences in the number of subrepeat elements.Comparison of rDNA restriction maps for two pea genotypes separated for hundreds or perhaps thousands of generations reveals that they contain many rDNA identical repeat units. This data is consistent with the view that new rDNA variants are fixed only infrequently in the evolution of a species.Differences also exist between the rDNA repeats of a single genotype with respect to the degree of base modification at certain restriction sites. A large number of sites known to exist in the pea rDNA clone are not cleaved at all in genomic rDNA, or are cleaved in only some copies of the rDNA repeat. We believe these examples of incomplete cleavage results mostly from methylation, although it is difficult to rule out the possibility of sequence variation in all cases. Most putative modifications are best interpreted in terms of cytosine methylation in CG and CXG sequences, but at least one example is more consistent with adenine methylation.We also have constructed a more detailed restriction map of the wheat rDNA clone pTA71 and present a comparison of this map to our map of pea, pumpkin, and wheat in order to assess the amount of useful evolutionary information that can be obtained by comparison of such maps.     

Phytochrome-mediated regulation of β-amylase mRNA level in mustard (Sinapis alba L.) cotyledons

Phytochrome, activated by continuous red light, increases the amount of total polyadenylated RNA during photomorphogenesis of mustard (Sinapis alba L.) cotyledons. In-vitro translation of total polyadenylated RNA in a reticulocyte translation system has shown that the activity of translatable -amylase mRNA is increased by phytochrome about threefold in the 3-d-old cotyledons, based on equal amounts of polyadenylated RNA, and about eightfold on a per-cotyledon basis. Cordycepin prevents the accumulation of translatable -amylase mRNA. It is concluded that the phytochrome-mediated control of -amylase synthesis is exerted on the level of mRNA synthesis. During seedling development in continuous red light, a phytochrome-dependent increase of -amylase mRNA can be observed at least 6 h before the onset of -amylase synthesis. If, after a period of enzyme synthesis, phytochrome action is interrupted by long-wavelength far-red light followed by darkness, -amylase mRNA as well as -amylase synthesis remain at a high level for 8–10 h and then decline sharply. It is concluded that -amylase mRNA, having an apparent lifetime of the order of 8–10 h, can be formed under the influence of phytochrome during early seedling development but it activates -amylase synthesis only after a lag-phase of about 8 h, when the cotyledons acquire competence to synthesize the enzyme. The consequences of these findings for the signal-transduction chain of phytochrome are discussed.Abbreviations EDTA Na₂-ethylenediaminotetraacetic acid - PAGE polyacrylamide gel electrophoresis - poly(A)⁺RNA polyadenylated mRNA - P_r, P_fr red- and far-red-absorbing forms of phytochrome - SDS sodium dodecyl sulfate - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Effect of cytokinins on ribosomal RNA gene expression in excised cotyledons of Cucurbita pepo L.

Excised pumpkin (Cucurbita pepo L.) cotyledons were used to investigate the effects of two different types of cytokinins: N⁶-benzyladenine and N₁-(2-chloro-4-pyridyl)-N₂-phenylurea on RNA synthesis in isolated nuclei. Treatment of cotyledons with both cytokinins resulted in a rapid enhancement of nuclear RNA-polymerase-I activity (EC 2.7.7.6). Maximum stimulation of RNA polymerase I, responsible for rRNA synthesis, was observed 4–6 h after the start of cytokinin action. The activity of RNA polymerase II was stimulated much more slowly and to a lesser extent. Uridine 5-monophosphate-uridine analysis of the alkalidigested nascent pre-rRNA chains showed that the stimulation of RNA-polymerase-I activity was the consequence of an increase of the polyribonucleotide-clongation rate. No significant change in the number of transcribing enzyme molecules was defected after hormone treatment (86·10³ RNA-polymerase-I molecules per diploid genome).Indications that de-novo protein synthesis is necessary for cytokinin-mediated RNA-polymerase stimulation were derived from experiments showing inhibition by cycloheximide.Abbreviations BA N⁶-benzyladenine - [PU]-30 N₁-(2-chloro-4-pyridyl)-N₂-phenylurea - UMP undine 5-monophosphate - UTP udine 5-triphosphate     

Characterization of a promoter up mutation in the -35 region of the promoter of the primer for ColE1 replication

Summary A point mutation in the -35 region of the promoter of the primer for initiation of DNA replication in the plasmid pMB1 was characterized. This base change causes a promoter up phenotype. The analysis of a second mutant obtained by site-directed mutagenesis allowed the exclusion of a role in the phenotype for the potential intrastrand secondary structure as well as for the methylation state of the DNA in the promoter region. The promoter up phenotype is concluded to be due to a change in the primary structure of the — 35 element with the consequent production of a better cluster of hydrogen bond donors and acceptors for the RNA polymerase.