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The plethora of actions of 1α,25(OH)2D3 in various systems suggested wide clinical applications of vitamin D nuclear receptor (VDR) ligands in treatments of inflammation, dermatological indication, osteoporosis, cancers, and autoimmune diseases. More than 3000 vitamin D analogues have been synthesized in order to reduce the calcemic side effects while maintaining the transactivation potency of these ligands. Here, we report the crystal structures of VDR ligand binding domain bound to two vitamin D agonists of therapeutical interest, calcipotriol and seocalcitol, which are characterized by their side chain modifications. These structures show the conservation of the VDR structure and the adaptation of the side chain anchored by hydroxyl moieties. The structure of VDR-calcipotriol helps us to understand the structural basis for for the switching of calcipotriol to a receptor antagonist by further side chain modification. The VDR-seocalcitol structure, in comparison with the structure of VDR-KH1060, a superagonist ligand closely related to seocalcitol, shows adaptation of the D ring and position of C-21 in order to adapt its more rigid side chain.

G-protein coupled receptors (GPCRs) constitute the largest set of cell membrane proteins involved in signal transduction and more than half of all drugs currently available influence their activity. Furthermore, genomic sequencing techniques have already enabled the isolation of more than hundred genes that encode so called orphan receptors representing a fruitful resource of potential targets for cellular signaling studies and novel drug discovery. This review focuses on recent progress in molecular cloning, gene organization analysis and chromosomal localization of a new sub-family of mammalian genes encoding the GPR37 (G-Protein coupled orphan Receptor 37) and related proteins. These genes are specifically expressed in brain tissues and they are significantly homologous to endothelin- and bombesin- receptor genes. Comparative genomic analysis has identified two distinct sets of highly conserved human and rodent genes. The first group includes the ortholog genes encoding the putative human, mouse a nd rat GPR37 receptors, also termed ETBR-LP (Endothelin-B Receptor-Like Protein) or GPCR / CNS1 (GPCR / Central Nervous System 1), that are characterised by a relatively large putative extracellular domain (261-249 amino-acids). The second group comprises the genes of the human, mouse and rat GPR37L1 [GPR37-Like protein 1 or ET(B)R-LP-2, GPCR / CNS2] with a shorter (129 amino-acids) extracellular domain. The human and mouse GPR37 and GPR37L1 genes have been shown to contain a single intron interrupting the receptor-coding sequence within the presumed third transmembrane domain. Northern blot analysis and in situ hybridization have shown characteristic patterns of expression of GPR37 and related genes suggesting that they may exert highly specific functions in the mammalian central nervous system.

A soluble cell-free extract derived from stage 6 Xenopus laevis oocytes is described. From supercoiled simian virus 40 DNA the extract produces nicked circles (having a single-strand scission), linear molecules of full unit size, shorter length fragments, and various forms of complex DNA.

A purified system is described for the introduction of negative supercoils into simian virus 40 DNA. The system consists of histones H2A, H2B, H3, and H4, DNA-relaxing enzyme, and a purified factor from Xenopus laevis stage 6 oocyte nuclei. The nuclei are prepared en masse by the technique of F. Scalenghe, M. Buscaglia, C. Steinheil, and M. Crippa [(1978) Chromosoma 60, 299-308]. The supercoiled simian virus 40 DNA prepared by this method is indistinguishable from simian virus 40 supercoiled DNA prepared from infected monkey cells.

We demonstrate that, when the yeast tRNA(3Leu) gene is stretched so that the distance between the two portions of the intragenic promoter is increased to 365 base pairs, the A and B blocks remain functional. Mutations in the A block, which show a weak phenotype when inserted in the wild type, exert a dramatic effect when inserted into the stretched gene. Experiments with extensively purified transcription factor tau indicate that the tau B-B block interaction is not influenced by A-B distance; only the ability of tau A to interact with A block sequences is affected, possibly because of the additional free-energy cost of forming a large loop of the intervening DNA.

A ribonuclease (RNase) activity, RNase "XlaI," responsible for the excision of intervening sequences from two yeast transfer ribonucleic acid (tRNA) precursors, pre-tRNA(Tyr) and pre-tRNA(3Leu), has been purified 54-fold from nuclear extracts of Xenopus laevis oocytes. The RNase preparation is essentially free of contaminating RNase. A quantitative assay for RNase XlaI was developed, and the reaction products were characterized. RNase XlaI cleavage sites in the yeast tRNA precursors were identical to those made by yeast extracts (including 3'-phosphate and 5'-hydroxyl termini). Cleavage of pre-tRNA(3Leu) by RNase XlaI and subsequent ligation of the half-tRNA molecules do not require removal of the 5' leader or 3' trailer sequences.

The phosphocellulose component of RNA polymerase binds the first nucleotide when synthesis of an RNA chain is initiated