A series of mutable alleles of the white locus in Drosophila melanogaster

Summary The origin and phenotypes of a number of zeste mutant stocks with mutable white loci are described. Each newly arising form was lighter in eye color than the mutant it originated from. In each case the lighter pigmentation is believed to be due to an increase in genetic material in the proximal region of the white locus, the increase supposedly being the result of unequal crossing over. Some of the mutations which arose in the mutable stocks are reversions. They occurred in males as well as in homo- and heterozygous females. The reversions are believed to be due to a decrease in genetic material in the proximal region of the white locus. The decrease is assumed to be the result of intrachromosomal recombination. At least some of these events took place premeiotically. New mutants which originate frequently from mutable stocks are stable. In addition to the structure of the mutable white locus there is probably at least one still unknown factor which affects its mutability since the frequency of mutations arising in the mutable stocks decreases over the years.     

Mechanism of activation of Sepharose and Sephadex by cyanogen bromide

The mechanism of CNBr activation of polysaccharide resins like Sepharose and Sephadex has been elucidated using recently published analytical procedures for the determination of cyanate esters and imido carbonates. It was found that on agarose-based resins coupling of ligand occurs predominantly via cyanate esters, and not via imidocarbonates as in the case of Sephadex. This explains the different behaviours of Sepharose and Sephadex during CNBr activation.     

Efficiency in cloning and sequencing using the single-stranded bacteriophage M13

A number of approaches to sequence DNA by the chain termination method are based on cloning into M13 phage vectors and the use of a universal primer. In this paper we investigate some of the factors which influence the speed and efficiency of these approaches. A modification of the template preparation, sequencing reaction, and gel system was used to obtain more reliable and clearer ladder gels. Redundancy and deficiency of shotgun DNA sequencing were reduced by a mapping technique and the use of synthetic primers. The mapping and cloning technique was used to organize the data entry so that the computer time necessary to reconstruct the sequence out of overlaps was reduced.     

Chromosomal investigations in children with pyknolepsy on dipropylacetate monotherapy

Summary We analyzed chromosome preparations obtained from leukocytes of ten children with pyknolepsy and treated with dipropylacetate (DPA) as monotherapy. Structural or numerical aberrations were not found more frequently in our patients than in five normal children (control group).     

Primer-directed mutagenesis of linearized plasmids

Two novel mutagenesis techniques to specifically alter the sequence of plasmid DNA have been developed. In contrast to other primer-directed mutagenesis methods which require a single-stranded, closed-circular template, a linearized single strand was used as the mutagenesis template. The template is prepared by restriction enzyme digestion of covalently-closed-circular plasmid DNA. These methods are simple, require small amounts of plasmid DNA, and can result in a relatively high frequency of mutagenesis.     

Immunohistochemical characterization of the thymic microenvironment

Summary The epithelial framework of the human thymus has been studied in parallel by immunohistochemical methods at the light- and electron-microscopic levels. Different monoclonal antibodies were used, reacting with components of the major histocompatibility complex, keratins, thymic hormones and other as yet antigenically undefined substances, which show specific immunoreactivities with human thymus epithelial cells.The electron-microscopic immunocytochemical observations clearly confirm microtopographical differences of epithelial cells not only between the thymic cortex and medulla, but also within the cortex itself. At least four subtypes of epithelial cells could be distinguished: 1) the cortical surface epithelium; 2) the main cortical epithelial cells and thymic nurse cells; 3) the medullary epithelial cells; and 4) the epithelial cells of Hassall's corpuscles.The various epithelial cell types of the thymus display several common features like tonofilaments, desmosomes and some surface antigens as demonstrated by anti-KiM3. In other respects, however, they differ from each other. The cortical subtype of thymic epithelial cells including the thymic nurse cells shows a distinct pattern of surface antigens reacting positively with antibodies against HLA-DR (anti-HLA-DR) and anti-21A62E. Electron-microscopic immunocytochemistry with these antibodies clearly reveals a surface labeling and a narrow contact to cortical thymocytes particularly in the peripheral cortical regions. An alternative staining pattern is realized by antibodies to some antigens associated with other subtypes of thymic epithelial cells. Medullary epithelial cells as well as the cortical surface epithelium react likewise positively with antibodies to special surface antigens (anti-Ep-1), to special epitopes of cytokeratin (anti-IV/82), and to thymic hormones (anti-FTS). The functional significance of distinct microenvironments within the thymus provided by different epithelial cells is discussed in view of the maturation of T-precursor cells.Glossary of Abbreviations Anti-X anti-X antibody - APUD-cells amine precursor uptake and decarboxylation (gastro-intestinal endocrine cells) - DAB diamino-benzidine - DMSO dimethyl sulfoxide - FTS facteur thymique sérique - HLA-A, B, C human leucocyte antigen, A, B, C-region related - HLA-DR human leucocyte antigen, D-region related - IDC interdigitating cell - MHC major histocompatibility gene complex - PBS phosphate-buffered saline - TNC thymic nurse cell This investigation was supported by grants from the Deutsche Forschungsgemeinschaft, and its Sonderforschungsbereich 111Fellow of the Alexander von Humbold-Stiftung, Institute of Pathology, University of Würzburg, Federal Republic of GermanyThe authors appreciate the contribution of human thymus tissue from Professor Alexander Bernhard, Abteilung kardiovasculäre Chirurgie der Universität Kiel; the gift of monoclonal antibodies from Dr. M.J.D. Anderson, Dr. M. Dardenne and Dr. H.J. Radzun; and the excellent technical assistence of Mrs. O.M. Bracker, Mrs. H. Hansen, Mrs. R. Köpke, Mrs. M. v. Kolszynski, Mrs. J. Quitzau, Mrs. H. Siebke, and Mrs. H. Waluk     

Spontaneous curvature of fluid vesicles induced by trans-bilayer sugar asymmetry

We present measurements of the effective spontaneous curvature of fluid lipid bilayers as a function of trans-bilayer asymmetry. Experiments are performed on micrometer-scale vesicles in sugar solutions with varying species across the membrane. There are two effects leading to a preferred curvature of such a vesicle. The spontaneous curvatures of the two monolayers as well as their area difference combine into an effective spontaneous curvature of the membrane. Our technique for measuring this parameter allows us to use vesicle morphology as a probe for general membrane-solute interactions affecting elasticity. Received: 3 June 1998 / Revised version: 18 August 1998 / Accepted: 21 August 1998