A study of histocompatibility-2 antigens in wild mice from Santiago,Chile

LyM-1 is the provisional designation given to a system of murine cell-surface alloantigens which are controlled by genes closely linked to those of theMls system. Formal genetic analysis has failed to disclose separation of genes determiningMls and LyM-1 antigens, but studies of the distribution of these antigens among inbred strains shows that the LyM-1 polymorphism is not primarily responsible for the MLR activity associated with Mls differences, and suggests that LyM-1 and Mls substances are products of genes at closely linked, but probably separate loci. Absorption analysis shows that strains whose cells react with anti-LyM-1.2 can be divided into at least two classes on the basis of the efficiency with which their cells remove anti-LyM-1.2 antibodies. This provides evidence for the existence of two LyM-1 alleles in addition to the one(s) possessed by nonreactive mouse strains.     

Instability of plasmid DNA sequences: Macro and micro evolution of the antibiotic resistance plasmid R6-5

Summary Detailed examination of the structure of cloned DNA fragments of the R6-5 antibiotic resistance plasmid has revealed a substantial degree of polynucleotide sequence heterogeneity and indicates that sequence rearrangements in plasmids and possibly other replicons occur more frequently than has hitherto been appreciated. The sequence changes in cloned R6-5 fragments were shown in some instances to have occurred prior to cloning, i.e. existed in the original population of R6-5 molecules that was obtained from a single bacterial clone and by several different criteria judged to be homogeneous,and in others to have occurred either during the cloning procedure or during subsequent propagation of hybrid molecules. The molecular changes that are described involved insertion/deletion of the previously characterized IS2 insertion element, formation of a new inverted repeat structure probably by duplication of a preexisting R6-5 DNA sequence, sequence inversion, and loss and gain of restriction endonuclease cleavage sites.     

Spatial and temporal gene expression patterns occur during corm development.

We investigated gene expression patterns that occur during taro corm development. Two-dimensional gel electrophoresis identified several different prevalent proteins that accumulate during corm development. Microsequencing studies indicated that some of these proteins are related to taste-modifying proteins, such as curculin and miraculin, and proteins found in other storage organs, such as sporamin and the Kunitz trypsin inhibitor. A curculin-encoding cDNA clone, designated as TC1, was identified that corresponds to a highly prevalent 1-kb corm mRNA. The TC1 mRNA accumulates during corm development, is more prevalent in corm apical than basal regions, and is either absent, or present at low concentrations, in other vegetative organs such as the leaf and root. In situ hybridization experiments showed that the TC1 mRNA is highly concentrated in corm storage parenchyma cells and is absent, or present in reduced concentrations, in other corm cells and tissues. Our results show that corm development is associated with the differentiation of specialized cells and tissues, and that these differentiation events are coupled with the temporal and spatial expression of corm-specific genes.     

Characterization of F-pilin as an inner membrane component of Escherichia coli K12.

Antipeptide antibodies were used to detect, purify, and characterize nonfilament F-pilin in the cell envelope of an F'tra+ strain of Escherichia coli. Affinity-purified goat antibodies raised against a peptide corresponding to the amino-terminal 14 amino acids of F-pilin detected F-pilin in immuno-overlay ("Western") blots of electrophoretically separated inner and outer membrane proteins. As expected, the molecule was absent from inner membrane preparations of F- or F'traA[Am] strains. Immunoreactive material was purified from inner membrane fractions and shown to be F-pilin by amino acid analysis. The anti-peptide antibodies also detected membrane forms of F-pilin produced by cells containing plasmid pTG801 (Grossman, T. & Silverman, P. (1989) J. Bacteriol. 171, 650-656). Most cell envelope pilin was in the inner membrane fraction, but a significant quantity fractionated with the outer membrane as well. The hydropathy profile of F-pilin suggested that the molecule is an integral membrane protein with two membrane-spanning domains. In confirmation, F-pilin and pTG801 pilins in inner membrane preparations were solubilized by a single extraction with the nonionic detergents Nonidet P-40 (2%) or Triton X-100 (2%), but not by 2 M KCl or 0.1 M NaOH. Moreover, analysis of traA'-'phoA constructs indicated that both the amino and carboxyl termini of F-pilin face the periplasm. The periplasmic location of the amino terminus was confirmed by immunoelectron microscopy of spheroplasts from F' and pTG801 strains, using a monoclonal antibody that recognizes an amino-terminal epitope. These data suggest a specific structure for membrane F-pilin. We discuss that structure in relation to the probable structure of filament F-pilin.     

Uridine transport in basolateral plasma membrane vesicles from rat liver

Summary The characteristics of uridine transport were studied in basolateral plasma membrane vesicles isolated from rat liver. Uridine was not metabolized under transport measurement conditions and was taken up into an osmotically active space with no significant binding of uridine to the membrane vesicles. Uridine uptake was sodium dependent, showing no significant stimulation by other monovalent cations. Kinetic analysis of the sodium-dependent component showed a single system with Michaelis-Menten kinetics. Parameter values were K _M 8.9 m and V _max 0.57 pmol/mg prot/sec. Uridine transport proved to be electrogenic, since, firstly, the Hill plot of the kinetic data suggested a 1 uridine: 1 Na⁺ stoichiometry, secondly, valinomycin enhanced basal uridine uptake rates and, thirdly, the permeant nature of the Na⁺ counterions determined uridine transport rates (SCN^– > NO ₃ ^– > Cl^– > SO ₄ ^2– ). Other purines and pyrimidines cis-inhibited and trans-stimulated uridine uptake.This work has been partially supported by grant PM90-0162 from D.G.I.C.Y.T. (Ministerio de Educación y Ciencia, Spain). B.R.-M. is a research fellow supported by the Nestlé Nutrition Research Grant Programme.     

Mechanical implications of in vivo human diaphragm shape.

Using magnetic resonance imaging, we measured the three-dimensional form of the diaphragm in vivo in four supine relaxed subjects at functional residual capacity and calculated its total surface area, the right and left surface areas in the zone of apposition, and the principal radii of curvature as a function of height. The area of apposition comprised 45 +/- 1.5% (SE) of the total surface area of the diaphragm. Available data on the area of the central tendon indicate that a considerable part of the muscular part of the diaphragm is lung apposed. The curvature was linearly related to height over 7 cm of the posterior half of each hemidiaphragm. From the linear portion of this graph and assuming a vertical gradient of transdiaphragmatic pressure of 0.75 cmH2O/cm, we applied the Laplace law and calculated tensions of 54 and 32 g/cm for right and left sides, respectively. We conclude that the shape of at least part of the posterior half of the relaxed human diaphragm in the supine position at functional residual capacity can be explained by the Laplace law, suggesting that both the lung and abdominal contents behave sufficiently as fluids so that they do not impose their shape on the diaphragm. Because diaphragm muscle is partly lung apposed, it is unlikely that the diaphragm functions simply as a piston.     

Influence of the carboxyl terminus of luteinizing hormone-releasing hormone and bradykinin on hydrolysis by brain endo-oligopeptidases

A homogeneous preparation of endo-oligopeptidase A from rabbit brain cleaves luteinizing hormone-releasing hormone (less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) at the Tyr-Gly bond only after the removal of Gly-NH2 from the COOH-terminal position of the molecule. The influence of the carboxyl terminus on hydrolysis by brain endo-oligopeptidases was studied using bradykinin as a model substrate. The substitution of the carboxyl group of bradykinin by the amide reduces by 2.5-fold the rate of Phe-Ser bond hydrolysis by endo-oligopeptidase A but has no effect on the rate of hydrolysis of the Pro-Phe bond by endo-oligopeptidase B. On the other hand, the deletion of Phe-Arg from the COOH-terminal portion of bradykinin makes the peptide resistant to hydrolysis by endo-oligopeptidase A whereas it increases by 5-fold the rate of hydrolysis of the Pro-Gly bond by endo-oligopeptidase B.     

Terpenes of Podocarpus lambertius

Sitosterol and the following terpenic compounds have been isolated from the bark of Podocarpus lambertius: 3β-hydroxytotarol, 4β-carboxynortotarol, and macrophyllic and lambertic acids. The leaves yielded sitosterol, stigmastan-3β,5α-diol-6-one, isopimaric acid, phyllocladene, isophyllocladene, 8,9-abieten-15-ol and 17-isophyllocladenol.