High irradiance response promotion of a subsequent light induction response in Sinapis alba L.

Relative quantum responsivity curves for inhibition of hypocotyl elongation in Sinapis alba L. seedlings previously grown in white light confirm that a marked end of day inhibition response can be induced by a monochromatic light treatment (30 min) at the end of the light period. In dark grown seedlings, however, no growth inhibition can be induced by a 30 min monochromatic light treatment. A prerequisite for an induction response appears to be a pretreatment with continuous light. Far red light is most effective with blue and red light showing a lesser effectiveness. The light pretreatment also shows a marked fluence rate dependency with respect to its ability to allow an induction response to manifest itself. The pretreatment required shows all the characteristics of a classical HIR response. The appearance of the effect in plants treated with the herbicide SAN 9789 seems to exclude chlorophyll as being the photoreceptor.Abbreviations SAN 9789 4-chloro-5-(methylamino)-2-(, , -trifluoro-m-tolyl)-3(2H)-pyridazinone - RG9 light long wavelength far red light (Schott RG9 colour glass) - FR far red light - WL white light - BL blue light - RL red light - D darkness - P_tot total phytochrome - P_fr far red absorbing form of phytochrome - HSR high irradiance response     

Interaction between a G-patch protein and a spliceosomal DEXD/H-box ATPase that is critical for splicing

Prp2 is an RNA-dependent ATPase that activates the spliceosome before the first transesterification reaction of pre-mRNA splicing. Prp2 has extensive homology throughout the helicase domain characteristic of DEXD/H-box helicases and a conserved carboxyl-terminal domain also found in the spliceosomal helicases Prp16, Prp22, and Prp43. Despite the extensive homology shared by these helicases, each has a distinct, sequential role in splicing; thus, uncovering the determinants of specificity becomes crucial to the understanding of Prp2 and the other DEAH-splicing helicases. Mutations in an 11-mer near the C-terminal end of Prp2 eliminate its spliceosome binding and splicing activity. Here we show that a helicase-associated protein interacts with this domain and that this interaction contributes to the splicing process. First, a genome-wide yeast two-hybrid screen using Prp2 as bait identified Spp2, which contained a motif with glycine residues found in a number of RNA binding proteins. SPP2 was originally isolated as a genetic suppressor of a prp2 mutant. In a reciprocal screen, Spp2 specifically pulled out the C-terminal half of Prp2. Mutations in the Prp2 C-terminal 11-mer that disrupted function or spliceosome binding also disrupted Spp2 interaction. A screen of randomly mutagenized SPP2 clones identified an Spp2 protein with a mutation in the G patch that could restore interaction with Prp2 and enhanced splicing in a prp2 mutant strain. The study identifies a potential mechanism for Prp2 specificity mediated through a unique interaction with Spp2 and elucidates a role for a helicase-associated protein in the binding of a DEXD/H-box protein to the spliceosome.     

Multiple different missense mutations in the pore region of HERG in patients with long QT syndrome

Long QT syndrome (LQTS), is an inherited cardiac disorder in which ventricular tachyarrhythmias predispose affected individuals to syncope, seizures, and sudden death. Characteristic electrocardiographic findings include a prolonged QT interval, T wave alternans, and notched T waves. We have screened LQTS patients from 89 families for mutations in the pore region of HERG , the K⁺ channel gene previously associated with chromosome 7-linked LQT2. In six unrelated LQTS kindreds, single-strand conformation polymorphism analyses identified aberrant conformers in all affected family members. These conformers were not seen in over 100 unaffected, unrelated control individuals, suggesting that they represent pathogenic LQTS mutations. DNA sequence analyses of the aberrant conformers demonstrated that they reflect five different missense mutations: V612L, A614V, N629D, N629S, and N633S. The missense mutation A614V was found in two unrelated families. Further functional studies will be required to determine what effect each of these changes may have on HERG channel function. Received: 15 July 1997 / Accepted: 10 November 1997     

Binding of ethylene analogs and cyclic olefins to a Triton X-100 extract from plants: Comparison with in vivo activities

The binding constants of various olefins were determined with a Triton X-100 extract of mung bean sprouts. The olefins tested included compounds that have been reported to induce an ethylene response in vivo as well as olefins reported to block the ethylene response. Both types of compounds were bound by the Triton X-100 extract, and the binding constants in vitro were usually considerably lower than those obtained in in vivo studies as measured by gas phase concentrations. Increased solubility due to Triton X-100 solution appears to be partly responsible. The in vitro binding order of compounds reported to induce an ethylene response was similar to their order of in vivo activity. Also, the compounds which gave an anti-ethylene response in vivo bound to the extract in approximately the same order as their in vivo effectiveness. These results suggest that binding of olefins is not the only factor necessary for an ethylene response. Although binding is necessary for activity, another factor must be involved after binding, and this may be -acceptance.     

UV-B Inhibition of Phytochrome-Mediated Anthocyanin Formation in Sinapis alba L. Cotyledons : Action Spectrum and the Role of Photoreactivation

An action spectrum was measured for ultraviolet (UV) radiation-induced damage to (inhibition of) phytochrome-induced anthocyanin formation in cotyledons of 40-hour-old Sinapis alba L. seedlings. The action spectrum showed maximum effectiveness in the 260 to 280 nanometer waveband with little effect above 295 nanometers. The damaging effect of UV could be photorepaired by subsequent exposure to sunlight or to long wavelength (360 nanometers) UV radiation. Because this form of damage is subject to photorepair (photoreactivation), it is probably due to the formation of pyrimidine dimers, and the results suggest that it would not be ecologically relevant even if there was an increase in solar UV due to a decrease in stratospheric ozone levels of about 30%. If a dark period of more than 1 hour is interspersed between the phytochrome induction and the UV irradiation, the inhibition of the phytochrome induction gradually decreases with increasing dark period.