NSR1 is required for pre-rRNA processing and for the proper maintenance of steady-state levels of ribosomal subunits.

NSR1 is a yeast nuclear localization sequence-binding protein showing striking similarity in its domain structure to nucleolin. Cells lacking NSR1 are viable but have a severe growth defect. We show here that NSR1, like nucleolin, is involved in ribosome biogenesis. The nsr1 mutant is deficient in pre-rRNA processing such that the initial 35S pre-rRNA processing is blocked and 20S pre-rRNA is nearly absent. The reduced amount of 20S pre-rRNA leads to a shortage of 18S rRNA and is reflected in a change in the distribution of 60S and 40S ribosomal subunits; there is no free pool of 40S subunits, and the free pool of 60S subunits is greatly increased in size. The lack of free 40S subunits or the improper assembly of these subunits causes the nsr1 mutant to show sensitivity to the antibiotic paromomycin, which affects protein translation, at concentrations that do not affect the growth of the wild-type strain. Our data support the idea that NSR1 is involved in the proper assembly of pre-rRNA particles, possibly by bringing rRNA and ribosomal proteins together by virtue of its nuclear localization sequence-binding domain and multiple RNA recognition motifs. Alternatively, NSR1 may also act to regulate the nuclear entry of ribosomal proteins required for proper assembly of pre-rRNA particles.     

Amino acid metabolism in several tissues of the obese Zucker rat as indicated by the tissue accumulation of α-amino[1-14C]isobutyrate

Measurements of the tissue accumulation of α-amino[1-¹⁴C]isobutyrate [1-¹⁴C]AIB) in lean (+/?) and obese (fa/fa) Zucker rats showed an augmented tissue/plasma ratio in the liver of the obese animals. In contrast, brown adipose tissue AIB accumulation was lower in the fa/fa animals. In response to a 24h starvation period AIB accumulation was significantly elevated in the liver and plasma of the lean animals and was unchanged in the liver of the fa/fa animals. The circulating concentration of alanine and branched-chain amino acids was elevated in the fa/fa animals as compared to their lean counterparts. These observations suggest that amino acid uptake is not involved in the impaired muscle development observed in the obese Zucker rat and that the ability of brown adipose tissue for amino acid utilization is decreased in the obese animals suggesting that this may partially explain the impaired thermoregulatory capacity observed in brown adipose tissue of obese Zucker rats.     

Distribution of histamine in the rat kidney during pregnancy and development

Summary An antiserum against conjugated histamine and two oligonucleotide probes that detect the mRNA encoding L-histidine decarboxylase (HDC) involved in histamine synthesis were used to study the appearance of histamine and its location in the kidneys of fetal, newborn and young postnatal rats and in the kidneys of pregnant rats. On embryonic days 16 and 18 (E16 and E18), some HA-immunoreactive (HA-ir) cells were found within the largest S-shaped bodies. Histamine was found to appear rapidly between the 18th and 20th embryonic days in the convoluted tubules of the kidneys. On postnatal day 0 (P0), the distal convoluted tubules and collecting ducts exhibited bright fluorescence, the intensity of which decreased quickly so that it was faint on day P4 and absent at later stages. In kidneys of pregnant rats HA-ir was found in the epithelium of both the Bowman's capsule, collecting ducts and in a few cells within the tubules. Nonuniform HA-ir was also detected within glomeruli. No evidence for the presence of L-histidine decarboxylase mRNA in kidneys of fetuses or pregnant rats was seen. It is concluded that distinct structures in the developing rat kidney contain histamine during a period around birth from day E20 to day P4. In the pregnant rat, the epithelium that is in direct contact with the urine flow is immunoreactive for histamine from day 16 to 20 of pregnancy. The results suggest that histamine is not synthesized locally in the kidneys but rather originates from other tissues.     

The polymorphism ApoB/4311 in patients with myocardial infarction and controls: the ECTIM study

Summary The polymorphism affecting codon 4311 of the apolipoprotein B gene (ApoB/4311) was investigated in a large case-control study in two French and one Northern Irish geographically defined populations. Cases were recruited 3 to 9 months after a myocardial infarction (MI) and controls were randomly selected from the population. The polymorphism was assessed using allele-specific oligonucleotides (ASO). The genotype frequencies of the ApoB/4311 polymorphism did not differ in Northern Ireland and France and were in Hardy-Weinberg equilibrium in all groups; strong associations with three other polymorphisms of the ApoB gene (XbaI, EcoRI, VNTR(34 repeats)) were observed and it was possible to identify highly sensitive and specific markers of the ApoB/4311 rare variant. Homozygotes for the ApoB 4311 rare variant were slightly less frequent in cases than in controls: 22 (4.4%) and 35 (6.7%) respectively (population adjusted ²=3.3 P<0.07), especially in Belfast: 6 (3.1%) and 12 (7.6%), respectively (P<0.06). Several lipid and lipoprotein parameters were measured. Consistently among control groups, rare homozygotes had lower mean levels of ApoB (P<0.02), triglycerides (P<0.02), and lipoprotein particles containing ApoE and ApoB (LpE:B; P<0.001) and a higher mean level of lipoprotein particles containing ApoAI and not ApoAII (LpAI; P<0.02) than heterozygotes and frequent homozygotes combined. The strong association between the ApoB/4311 polymorphism and LpE:B was also observed in patients with MI. When present in the homozygous form, the ApoB/ 4311 AsnSer variant is associated with a lipoprotein profile that is apparently favourable.     

Variants of the anti-Müllerian hormone gene in a compound heterozygote with the persistent Müllerian duct syndrome and his family

Summary The human genome contains a large number of interspersed simple repeat sequences that are variable in length and can therefore serve as highly informative, polymorphic markers. Typing procedures include conventional multilocus and single locus probing, and polymerase chain reaction aided analysis. We have identified simple sequences in a cosmid clone stemming from the human Y chromosome and consisting of (gata)_n repeats. We have compared these with two equivalent simple repeat loci from chromosome 12. After amplifying the tandemly repeated motifs, we detected between four and eight different alleles at each of the three loci. Codominant inheritance of the alleles was established in family studies and the informativity of the simple repeat loci was determined by typing unrelated individuals. The polymorphisms are suitable for application in linkage studies, practical forensic case work, deficiency cases in paternity determination, and for studying ethnological questions. The mutational mechanisms that bring about changes in simple repeats located both on the autosomes and on the sex chromosomes, are discussed.Professor Dr. Otto Prokop (Humboldt-Universität Berlin) on the occasion of his 70th birthday     

Expression, isolation and purification of antibody fragments fused to maltose-binding protein in Escherichia coli]

We have fused the variable domains of a mouse antibody to the C-terminal end of the maltose-binding protein (malE), at the genetic level. The hybrid proteins were expressed in E. coli under control of the malEp promoter, and exported to the periplasm, at low temperature. They were purified by affinity chromatography on cross-linked amylose. When the two variable domains were fused together through a peptide link, the hybrid displayed similar affinity and specificity to the antigen as the native antibody.     

Molecular characterization and genetic origin of the Brassica napus acetohydroxyacid synthase multigene family

Summary The Brassica napus rapeseed cultivar Topas contains an acetohydroxyacid synthase (AHAS) multigene family consisting of five members (AHAS 1–5). DNA sequence analysis indicate that AHAS1 and AHAS3 share extensive homology. They probably encode the AHAS enzymes essential for plant growth and development. AHAS2 has diverged significantly from AHAS1 and AHAS3 and has unique features in the coding region of the mature polypeptide, transit peptide and upstream non-coding DNA, which raises the possibility that it has a distinct function. AHAS4 and AHAS5 have interrupted coding regions and may be defective. The complexity of the AHAS multigene family in the allotetraploid species B. napus is much greater than reported for Arabidopsis thaliana and Nicotiana tabacum. Analysis of the presumptive progenitor diploid species B. campestris and B. oleracea indicated that AHAS2, AHAS3 and AHAS4 originate from the A genome, whereas AHAS1 and AHAS5 originate from the C genome. Further variation within each of the AHAS genes in these species was found.     

Differential accumulation of hydroxyproline-rich glycoproteins in bean root nodule cells infected with a wild-type strain or a C4-dicarboxylic acid mutant of Rhizobium leguminosarum bv. phaseoli

An antiserum raised against deglycosylated hydroxyproline-rich glycoproteins (HPGPs) from melon (Cucumis melo L.) was used to study the relationship between Rhizobium infection and induction of HRGPs in bean (Phaseolus vulgaris L.) root nodule cells infected with either the wild-type or a C₄-dicarboxylic acid mutant strain of Rhizobium leguminosarum bv. phaseoli. In effective nodules, where fixation of atmospheric dinitrogen is taking place, HRGPs were found to accumulate mainly in the walls of infected cells and in peribacteroid membranes surrounding groups of bacteroids. Internal ramifications of the peribacteroid membrane were also enriched in HRGPs whereas the peribacteroid space as well as the bacteroids themselves were free of these glycoproteins. In mutant-induced root nodules, HRGPs were specifically associated with the electron-dense, laminated structures formed in plastids as a reaction to infection by this mutant. The presence of HRGPs was also detected in the host cytoplasm. The aberrant distribution of HRGPs in infected cells of mutant-induced nodules likely reflects one aspect of the altered host metabolism in relation to peribacteroid-membrane breakdown. The possibility that the antiserum used for HRGP localization may have cross-reacted with ENOD 2 gene products is discussed in relation to amino-acid sequences and sites of accumulation.     

Mass-spectrometric determination of O2 and CO2 gas exchange in illuminated higher-plant cells

In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO₂ and O₂ gas exchange were performed using ¹⁸O₂, ¹³CO₂ and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O₂ and CO₂. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO₂), the rate of CO₂ influx represented 75±5% of the rate of gross O₂ evolution. After a dark-to-light transition, the rate of CO₂ efflux was inhibited by 50% whereas the O₂-uptake rate was little affected. The effect of a recycling of respiratory CO₂ through photosynthesis on the exchange of CO₂ gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO₂ recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO₂ efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO₂ efflux and O₂ uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO₂-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation.Abbreviations Chl chlorophyll - K_d permeability coefficient The authors thank Drs A. Vermeglio and P. Thibault, Dépt. de Biologie, CEN-Cadarache, St. Paul Lez Durance, France, for helpful discussions.