Nip7p interacts with Nop8p, an essential nucleolar protein required for 60S ribosome biogenesis, and the exosome subunit Rrp43p

NIP7 encodes a conserved Saccharomyces cerevisiae nucleolar protein that is required for 60S subunit biogenesis (N. I. T. Zanchin, P. Roberts, A. DeSilva, F. Sherman, and D. S. Goldfarb, Mol. Cell. Biol. 17:5001-5015, 1997). Rrp43p and a second essential protein, Nop8p, were identified in a two-hybrid screen as Nip7p-interacting proteins. Biochemical evidence for an interaction was provided by the copurification on immunoglobulin G-Sepharose of Nip7p with protein A-tagged Rrp43p and Nop8p. Cells depleted of Nop8p contained reduced levels of free 60S ribosomes and polysomes and accumulated half-mer polysomes. Nop8p-depleted cells also accumulated 35S pre-rRNA and an aberrant 23S pre-rRNA. Nop8p-depleted cells failed to accumulate either 25S or 27S rRNA, although they did synthesize significant levels of 18S rRNA. These results indicate that 27S or 25S rRNA is degraded in Nop8p-depleted cells after the section containing 18S rRNA is removed. Nip7p-depleted cells exhibited the same defects as Nop8p-depleted cells, except that they accumulated 27S precursors. Rrp43p is a component of the exosome, a complex of 3'-to-5' exonucleases whose subunits have been implicated in 5.8S rRNA processing and mRNA turnover. Whereas both green fluorescent protein (GFP)-Nop8p and GFP-Nip7p localized to nucleoli, GFP-Rrp43p localized throughout the nucleus and to a lesser extent in the cytoplasm. Distinct pools of Rrp43p may interact both with the exosome and with Nip7p, possibly both in the nucleus and in the cytoplasm, to catalyze analogous reactions in the multistep process of 60S ribosome biogenesis and mRNA turnover.     

Crystal structure of the iron-dependent regulator (IdeR) from Mycobacterium tuberculosis shows both metal binding sites fully occupied

Iron-dependent regulators are a family of metal-activated DNA binding proteins found in several Gram-positive bacteria. These proteins are negative regulators of virulence factors and of proteins of bacterial iron-uptake systems. In this study we present the crystal structure of the iron-dependent regulator (IdeR) from Mycobacterium tuberculosis, the causative agent of tuberculosis. The protein crystallizes in the hexagonal space group P62 with unit cell dimensions a=b=92.6 A, c=63.2 A. The current model comprises the N-terminal DNA-binding domain (residues 1-73) and the dimerization domain (residues 74-140), while the third domain (residues 141-230) is too disordered to be included. The molecule lies on a crystallographic 2-fold axis that generates the functional dimer. The overall structure of the monomer shares many features with the homologous regulator, diphtheria toxin repressor (DtxR) from Corynebacterium diphtheriae. The IdeR structure in complex with Zinc reported here is, however, the first wild-type repressor structure with both metal binding sites fully occupied. This crystal structure reveals that both Met10 and most probably the Sgamma of Cys102 are ligands of the second metal binding site. In addition, there are important changes in the tertiary structure between apo-DtxR and holo-IdeR bringing the putative DNA binding helices closer together in the holo repressor. The mechanism by which metal binding may cause these structural changes between apo and holo wild-type repressor is discussed.     

The exosome subunit Rrp43p is required for the efficient maturation of 5.8S, 18S and 25S rRNA

The Saccharomyces cerevisiae protein Rrp43p co-purifies with four other 3'-->5' exoribonucleases in a complex that has been termed the exosome. Rrp43p itself is similar to prokaryotic RNase PH. Individual exosome subunits have been implicated in the 3' maturation of the 5.8S rRNA found in 60S ribosomes and the 3' degradation of mRNAs. However, instead of being deficient in 60S ribosomes, Rrp43p-depleted cells were deficient in 40S ribosomes. Pulse-chase and steady-state northern analyses of pre-RNA and rRNA levels revealed a significant delay in the synthesis of both 25S and 18S rRNAs, accompanied by the stable accumulation of 35S and 27S pre-rRNAs and the under-accumulation of 20S pre-rRNA. In addition, Rrp43p-depleted cells accumulated a 23S aberrant pre-rRNA and a fragment excised from the 5' ETS. Therefore, in addition to the maturation of 5.8S rRNA, Rrp43p is required for the maturation 18S and 25S rRNA.     

Physical properties of optical fiber sidetap grating filters:free-space model

Presents theoretical and experimental results on the wavelength properties of sidetap grating filters written in single-mode optical fibers. A simple theoretical model based on Fraunhofer diffraction and antenna theory is used, modified to take into account the longitudinal variation of the incident field. Expressions are derived for the filter attenuation and bandwidth, and good agreement is demonstrated with experiment. The results show that the shape of the attenuation spectrum does not change with the filter length or index modulation, but that the magnitude of the attenuation increases with both parameters. The results also show that the effect of decreasing the fiber core-cladding index difference is to increase the peak attenuation and reduce the filter bandwidth. The existence of a strict longitudinal phase-matching condition is shown to cause asymmetry in the shape of the spectrum. Comparison with the properties of bulk sidetap gratings shows there to be a shift in the peak wavelength and apodization of the filter sidelobes. A simple diagram for the design of sidetap filters is presented for the first time     

Control of respiration as a means of controlling responses to threat.

111 undergraduates assessed the degree to which persons' physiological and psychological responses in a threatening situation might be altered by controlling respiration. Ss who (a) had a history of cardiac disease, (b) were taking medication that would influence heart rate, or (c) were engaged in any form of meditation were excluded from the study. After a 30-min rest period, Ss in a respiration-tracing condition began replicating their breathing patterns from the rest period; Ss in an attention-tracing condition participated in a comparable task that did not involve the control of respiration; and Ss in a no-tracing condition were not assigned any task. After the tracing manipulation was introduced, half of the Ss were assigned to a threat condition and informed that they would receive a series of painful electric shocks; the other Ss were assigned to a no-threat condition and informed that they would receive red light stimulation. Analyses of heart-rate and self-report data indicated that (a) the threat manipulation was effective; (b) controlling respiration did not reduce Ss' stress responses; and (c) Ss in the no-tracing condition were the only stressed Ss to show decreases in physiological arousal over time, an effect that may have been due to their use of a cognitive coping strategy. Findings do not provide evidence that control of respiration is an effective strategy for controlling stress but do suggest that, when not interfered with, Ss can employ relatively effective, self-generated cognitive coping strategies. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of fatty acid metabolism by glucagon in man. IV. Effects of a physiologic hormone infusion in normal man

This study was done to explore the role of physiologic elevations of glucagon concentration in plasma ketone body concentration in normal man. During the period of hormone elevation, plasma free fatty acids were pharmacologically elevated to ensure adequate free fatty acid substrate delivery to the liver to support hepatic ketogenesis. Eighty-minute infusions of glucagon resulted in a plasma hormone concentration of approximately 300 pg./ml. During the infusion, ketone bodies declined from their basal concentration and remained below basal for the duration of the infusion. An acute heparin-induced pharmacologic elevation of plasma free fatty acid concentration resulted in a transient rise in plasma ketone body concentration, but at no time did it attain the concentration observed during the control saline infusion. Plasma glucose concentration was not altered by glucagon infusion, but plasma insulin concentration rose by approximately 2.5 muU./ml. These results suggest that glucagon is not ketogenic in normal man as has been previously reported in insulin-deficient diabetics. The glucagon-induced rise in plasma insulin concentration may participate in the observed reduction in plasma ketone body concentration.     

Expression of interpersonal aggression by angered and nonangered persons with the Type A and Type B behavior patterns.

37 male undergraduates, who were classified on the student version of the Jenkins Activity Survey as showing the Type A (coronary prone) or Type B (noncoronary prone) behavior pattern, were first either angered or not angered in a problem-solving task by a confederate who posed as another S. In a subsequent bogus learning experiment, Ss had the opportunity to punish or reward the confederate. The effectiveness of the anger manipulation was attested to by the fact that angered Ss had reliably higher pulse rates and blood pressure. In the learning experiment, Type As who had not been angered gave the confederate reliably higher levels of punishment than did Type Bs, but there was no difference in the levels of punishment given by Type A and Type B Ss who had been angered. There was also no difference between Type A and Type B Ss in the levels of reward they gave the confederate. Results provide behavioral evidence for aggression in persons with the Type A behavior pattern. The fact that the difference in aggression was limited to nonangered Ss is interpreted in terms of differences in attributions of responsibility. (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mouse hepatitis virus receptor activities of an MHVR/mph chimera and MHVR mutants lacking N-linked glycosylation of the N-terminal domain

Mouse hepatitis virus binds to the N-terminal domain of its receptor, MHVR, a murine biliary glycoprotein with four immunoglobulin-like domains (G.S. Dveksler, M. N. Pensiero, C. W. Dieffenbach, C. B. Cardellichio, A.A. Basile, P.E. Elia, and K. V. Holmes, Proc. Natl. Acad. Sci. USA 90:1716-1720, 1993). A recombinant protein with only the anchored N-terminal domain was not a functional receptor, but a recombinant protein with the N-terminal domain of MHVR linked to the second and third immunoglobulin-like domains and anchor from the mouse poliovirus receptor homolog, mph, was a functional receptor for mouse hepatitis virus. The native four-domain MHVR has 16 potential N-linked glycosylation sites, including three on the N-terminal domain. Recombinant proteins lacking each one of these three sites or all three of them were functional receptors. Thus, glycosylation of the N-terminal domain is not required, but a glycoprotein longer than the N-terminal domain is required for virus receptor activity.