237 research outputs found
Iresine ajuscana Suess. & Beyerle in Repert. Spec.
No full textIresine ajuscana Suess. & Beyerle in Repert. Spec. Nov. Regni Veg. 39: 10. 1935 ≡ Iresine ajuscana f. longiflora Suess. in Repert. Spec. Nov. Regni Veg. 39: 10. 1935 – Holotype for I. ajuscana and Lectotype for I. ajuscana f. longiflora (designated here): MEXICO. Staat Mexico: Thal von Ajusco, 1870, L. Hahn 35 (B barcode B 10 0177104! [image!]; isotype/isolectotype: fragment M barcode M-0098602 [image!]). = Iresine ajuscana f. minutiflora Suess. in Repert. Spec. Nov. Regni Veg. 39: 11. 1935 – Lectotype (designated here): MEXICO. Sallo de aqua, Dec 1905, C.A. Purpus 1807 (B barcode B 10 0715445! [image!]). = Iresine grandis var. glabrata Suess. in Mitt. Bot. Staatssamml. München 4: 108. 1952 – Holotype: MEXICO. Oaxaca: Ayutla, Cañon Rio Tlahuitoltepec, 19–27 Feb 1937, W.H. Camp 2720 (NY barcodes 01259979! [image!]; isotype: NY barcode 01259978! [image!]). = Iresine rubella Suess. in Mitt. Bot. Staatssamml. München 4: 109. 1952 – Holotype: MEXICO. Mexico-Valle, Monte de la Parada, 1856–1858, s.coll. s.n. (BM!). Note. – The original description of the species has no f. ajuscana but Suessenguth created f. longiflora for the type specimen of the species. With the lectotypification we want to make sure that f. longiflora refers to the same specimen as the autonym. Forma longiflora then falls into the synonymy of the autonym and the specimen Hahn 35 at B is taken as the holotype for the species name. Regarding to f. minutiflora four specimens are mentioned as original material. Only the two plants collected by Purpus (nos. 1803 and 1807) were annotated by Suessenguth in 1934 with “ Iresine ajuscana f. minutiflora Suess. & Bey.” and are staminate plants. Because of the strong link, one of them is designated as lectotype. The two specimens from Amecameca, Sacro Monte 2300 m, 3-3-1932, H. Fröderström & E. Hultén 1207 und 1208, both collected on the same day and representing staminate and pistillate plants, lack any sign of the name of the form and were identified one year later, in 1935, by Suessenguth already citing the publication in the Repertorium The specimen described by Suessenguth (1952) as I. rubella has relatively well developed pistillodes but these lack functional filiform stigmas and contrary to the view of this author is interpreted as a staminate individual. Taxonomic status: Not a monophylum as currently defined, requires further study (C).Published as part of Thomas Borsch, Hilda Flores-Olvera, Silvia Zumaya & Kai Müller, 2018, Pollen characters and DNA sequence data converge on a monophyletic genus Iresine (Amaranthaceae, Caryophyllales) and help to elucidate its species diversity, pp. 944-976 in Taxon 67 (5) on pages 963-964, DOI: 10.12705/675.7, http://zenodo.org/record/148831
Tetracycline aptamer-controlled regulation of pre-mRNA splicing in yeast
No full textSplicing of pre-mRNA is a critical step in mRNA maturation and disturbances cause several genetic disorders. We apply the synthetic tetracycline (tc)-binding riboswitch to establish a gene expression system for conditional tc-dependent control of pre-mRNA splicing in yeast. Efficient regulation is obtained when the aptamer is inserted close to the 5′splice site (SS) with the consensus sequence of the SS located within the aptamer stem. Structural probing indicates limited spontaneous cleavage within this stem in the absence of the ligand. Addition of tc leads to tightening of the stem and the whole aptamer structure which probably prevents recognition of the 5′SS. Combination of more then one aptamer-regulated intron increases the extent of regulation leading to highly efficient conditional gene expression systems. Our findings highlight the potential of direct RNA–ligand interaction for regulation of gene expression
Conformational dynamics of the tetracycline-binding aptamer
No full textThe conformational dynamics induced by ligand binding to the tetracycline-binding aptamer is monitored via stopped-flow fluorescence spectroscopy and time-correlated single photon counting experiments. The fluorescence of the ligand is sensitive to changes within the tertiary structure of the aptamer during and after the binding process. In addition to the wild-type aptamer, the mutants A9G, A13U and A50U are examined, where bases important for regulation are changed to inhibit the aptamer’s function. Our results suggest a very fast two-step-mechanism for the binding of the ligand to the aptamer that can be interpreted as a binding step followed by a reorganization of the aptamer to accommodate the ligand. Binding to the two direct contact points A13 and A50 was found to occur in the first binding step. The exchange of the structurally important base A9 for guanine induces an enormous deceleration of the overall binding process, which is mainly rooted in an enhancement of the back reaction of the first binding step by several orders of magnitude. This indicates a significant loss of tertiary structure of the aptamer in the absence of the base A9, and underlines the importance of pre-organization on the overall binding process of the tetracycline-binding aptamer
Thermodynamic characterization of an engineered tetracycline-binding riboswitch
No full textRiboswitches reflect a novel concept in gene regulation that is particularly suited for technological adaptation. Therefore, we characterized thermodynamically the ligand binding properties of a synthetic, tetracycline (tc)-binding RNA aptamer, which regulates gene expression in a dose-dependent manner when inserted into the untranslated region of an mRNA. In vitro, one molecule of tc is bound by one molecule of partially pre-structured and conformationally homogeneous apo-RNA. The dissociation constant of 770 pM, as determined by fluorimetry, is the lowest reported so far for a small molecule-binding RNA aptamer. Additional calorimetric analysis of RNA point mutants and tc derivatives identifies functional groups crucial for the interaction and including their respective enthalpic and entropic contributions we can propose detailed structural and functional roles for certain groups. The conclusions are consistent with mutational analyses in vivo and support the hypothesis that tc-binding reinforces the structure of the RNA aptamer, preventing the scanning ribosome from melting it efficiently
Splicing-based synthetic gene circuits for universal logic computation in mammalian cells
No full text
Engineered riboswitches control gene expression by small molecules.
No full textWe have developed conditional gene expression systems based on engineered small-molecule-binding riboswitches. Tetracycline-dependent regulation can be imposed on an mRNA in yeast by inserting an aptamer in its 5'-untranslated region. Biochemical and genetic analyses determined that binding of the ligand tetracycline leads to a pseudoknot-like linkage within the aptamer structure, thereby inhibiting the initial steps of translation. A second translational control element was designed by combining a theophylline aptamer with a communication module for which a 1 nt slipping mechanism had been proposed. This structural element was inserted close to the bacterial ribosomal binding site at a position just interfering with translation in the non-ligand-bound form. Addition of the ligand then shifts the inhibitory element to a distance that permits efficient translation
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