Different conformational forms of Escherichia coli and rat liver 5S rRNA revealed by Pb(II)-induced hydrolysis.

Different stable forms of Escherichia coli and rat liver 5S rRNA have been probed by Pb(II)-induced hydrolysis. In the native A forms of 5S rRNA, Pb2+ reveal single-stranded RNA stretches and regions of increased conformational flexibility or distorted by the presence of bulged nucleotides. Hydrolysis of urea/EDTA-treated E. coli 5S rRNA (B form) shows the presence of two strong helical domains; helix A retained from the A form and a helix composed of RNA regions G33-C42 and G79-C88. Other RNA regions resistant to hydrolysis may be involved in alternative base pairing, causing conformational heterogeneity of that form. Pb(II)-induced hydrolysis distinguishes two different forms of rat liver 5S rRNA; the native A form and the form obtained by renaturation of 5S rRNA in the presence of EDTA. Pb(II)-hydrolysis data suggest that both forms are highly structured. In the latter form, the orientation of the bulged C66 is changed with respect to helix B. At the same time, a new helical segment is possibly formed, composed of nucleotides from helix C and loop c on one side and from helix E and loop d' on the other.     

Specific in vitro O-glycosylation of human granulocyte-macrophage colony-stimulating-factor-derived peptides by O-glycosyltransferases of yeast and rat liver cells.

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) is O-glycosylated at residues Ser9 and Thr10 during secretion by yeast and COS-1 cells [Ernst, J.F., Mermod, J.-J. and Richman, L.I. (1992) Eur. J. Biochem. 203, 663-667]. Two types of octapeptides encompassing residues 4-11 (peptide 4-11) and variants thereof, or residues 8-15 (peptide 8-15) of hGM-CSF were tested as substrates for in vitro O-glycosylation using dolichyl-phosphate- D-mannose: protein O-D-mannosyltransferase (Man-transferase) of the yeast Saccharomyces cerevisiae, or UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase (GalNAc-transferase) of rat liver cells. Peptide 8-15 was found to be O-glycosylated at residues Ser9 and Thr10 by GalNAc-transferase and, with reduced efficiency, also by Man-transferase. Peptide 4-11 was a good substrate for yeast Man-transferase, leading to mannosylation of only Thr10, whereas it was very poorly O-glycosylated at positions Ser5 and Ser7 by GalNAc-transferase. The observed differences in peptide-acceptor activities indicate that the site of O-glycosylation depends on similar, but not identical protein structural features in yeast and mammalian cells.     

Structural analysis of three prokaryotic 5S rRNA species and selected 5S rRNA--ribosomal-protein complexes by means of Pb(II)-induced hydrolysis.

Lead ions have been applied to the structural analysis of 5S rRNA from Thermus thermophilus, Bacillus stearothermophilus and Escherichia coli. Based on the distribution of Pb(II)-induced cleavages, some minor modifications of the consensus secondary structure model of 5S rRNA are proposed. They include the possible base pairing between nucleotides at positions 11 and 109, as well as changes in secondary interactions within the helix B region. The 'prokaryotic arm' region is completely resistant to hydrolysis in the three RNA species, suggesting that it is a relatively stable, highly ordered structure. Hydrolysis of E. coli 5S rRNA complexed with ribosomal protein L18 shows, besides the shielding effect of the bound protein, a highly enhanced cleavage between A108 and A109. It supports the concept that the major L18-induced conformational change involves the junction of helices A, B and D.     

Bone morphogenetic protein 4 (BMP-4), a member of the TGF-beta family, in early embryos of Xenopus laevis: analysis of mesoderm inducing activity

We have screened a Xenopus ovary cDNA library using a synthetic oligonucleotide derived from that part of the inhibin beta A sequence, which is highly conserved within the TGF-beta family. Out of several clones yielding autoradiographic signals four turned out to represent Xenopus counterparts to the human bone morphogenetic protein 4 (BMP-4). Each two of the four sequences are nearly identical and probably account for different alleles whereas the two pairs showing 5% divergence may have arisen by genome duplication in this tetraploid species. The amino acid sequence of the Xenopus protein is 80% homologous to the human sequence showing no single exchange within the last 100 amino acids at the C-terminus. This region, which constitutes the main part of the mature, biologically active protein, also exhibits substantial homologies to other representatives of the TGF-beta family, especially to the Drosophila DPPC protein. Transfection of COS-1 cells with the Xenopus BMP-4 sequence under control of the CMV-promoter leads to the secretion of a protein which exhibits mesoderm inducing activity when tested with animal cap explants from Xenopus blastula stage embryos.     

Structural analysis of plant ribosomal 5S RNAs. Visualisation of novel tertiary interactions by cleavage of lupin and wheat 5SrRNAs with ribonuclease H

A model for the tertiary structure of plant 5S rRNA, previously proposed by our laboratory (Joachimiak, A. et al. (1990) Int. J. Biol. Macromol., in press) was tested by specific cleavage of the plant 5S rRNA in the presence of synthetic oligodeoxynucleotides. The hexanucleotides used in this study were complementary to different portions of loops C, D and E, the nucleotides of which have recently been proposed to be involved in tertiary hydrogen bonds. The results obtained strongly support the interaction of loops C and D by nucleotides C34, C35, C36, A37 and G85, G86, G87, U88, respectively. Digestion pattern of loop E (domain gamma, nucleotides 66-110) suggests a possible different arrangement of this part of the plant 5S rRNA molecule, when compared with other eukaryotes.     

Translation initiation factor-dependent extracts from Saccharomyces cerevisiae

Translation initiation factor 4A- and 4E-dependent extracts were developed from Saccharomyces cerevisiae and used to study factor requirements for translation of individual mRNAs in vitro. Whereas all mRNAs tested required eIF-4A, mRNAs devoid of secondary structure in their 5' untranslated region did not require exogenous eIF-4E for translation. The latter included alfalfa mosaic virus RNA4, mRNA containing the untranslated region of tobacco mosaic virus RNA and mRNA containing part of the untranslated region of poliovirus RNA. Furthermore, initiation of translation on mRNAs containing part of the untranslated region of poliovirus RNA is most likely internal.     

Molecular cloning and expression of the cDNA for a novel alpha 1-adrenergic receptor subtype

A novel alpha 1-adrenergic receptor subtype has been cloned from a bovine brain cDNA library. The deduced amino acid sequence is that of a 466-residue polypeptide. The structure is similar to that of the other adrenergic receptors as well as the larger family of G protein-coupled receptors that have a presumed seven-membrane-spanning domain topography. The greatest sequence identity of this receptor protein is with the previously cloned hamster alpha 1B-adrenergic receptor being approximately 72% within the presumed membrane-spanning domains. Localization on different human chromosomes provides evidence that the bovine cDNA is distinct from the hamster alpha 1B-adrenergic receptor. The bovine cDNA clone expressed in COS7 cells revealed 10-fold higher affinity for the alpha 1-adrenergic antagonists WB4101 and phentolamine and the agonist oxymetazoline as compared with the alpha 1B receptor, results similar to pharmacologic binding properties described for the alpha 1A receptor. Despite these similarities in pharmacological profiles, the bovine alpha 1-adrenergic receptor is sensitive to inhibition by the alkylating agent chloroethylclonidine unlike the alpha 1A-adrenergic receptor subtype. In addition, a lack of expression in tissues where the alpha 1A subtype exists suggests that this receptor may actually represent a novel alpha 1-adrenergic receptor subtype not previously appreciated by pharmacological criteria.     

Acetylcholine--inhibition of transmitter release from adrenergic nerve terminals mediated by muscarinic receptors.

The evidence is reviewed for the presence of muscarinic receptors on the sympathetic nerves to blood vessels. Activation of these receptors by acetylcholine in doses that are too small to affect the smooth muscle cells directly inhibits the release of norepinephrine evoked by electric impulses or potassium ions. This inhibitory action of acetylcholine is prevented by muscarinic blocking agents and is probably due to hyperpolarization of the adrenergic nerve terminals.