Effect of Tween 80 on lipid vesicle permeability

As part of an examination of procedures for protein/lipid reconstitution we incubated solubilized cytochrome oxidase at different temperatures with preformed vesicles composed of saturated lipids. We observed that the 22Na permeability of these vesicles was increased following such an incubation step, with the maximal effect occurring following incubations at temperatures in the vicinity of the lipid gel to liquid-crystal phase change. However, these permeability changes could be completely duplicated by incubating similar vesicles with concentrations of Tween 80 used to solubilize the extracted oxidase. Thus detergent molecules used to solubilize extracted membrane proteins can induce significant changes in the reconstituting lipid environment and the possibility of such changes must be taken into account when interpreting the properties of the reconstituted lipid/protein system under study.     

Impact of introduction of colposcopy to a district general hospital.

During the first 18 months of operation of a new colposcopy clinic, established in a district general hospital, 608 women were seen. Most (568 (93.0%] were referred from within the local district, on the whole by their general practitioner. In 466 cases a repeat cervical smear was taken, and all women underwent colposcopic examination together with directed punch biopsy of any abnormal area. Positive cytology was seen in 356 women, but 85 (23.9%) of these were found to have no histological evidence of malignancy or premalignancy and were consequently discharged from the clinic. Cervical intraepithelial neoplasia was confirmed histologically in 379 women, of whom 259 were under 35 and 175 nulliparous. As a result of the use of colposcopy and local destructive methods of treatment only 42 patients (11.1%) were required to undergo cone biopsy. The initial overall incidence of success in the treatment of cervical intraepithelial neoplasia was 86.2% for cone biopsy, 88.5% for diathermy, and 81.1% for laser ablative treatment. Colposcopy has an important role in the management of cervical neoplasia in the district general hospital.     

Cholesterol-multilipid interactions in bilayers

To extend our knowledge of model membrane systems based upon one lipid component, multi-lamellar bilayers were made of cholesterol with two phospholipids in equimolar ratio, and the enthalpy change delta H of the main phase transition of the temary mixture was measured by differential scanning calorimetry (DSC) as a function of increasing cholesterol concentration c. The lipids were saturated phosphatidylcholines CnPC of acyl chain length n, and as the n of the two lipids became more different (from C13PC/C14PC to C14PC/C15PC to C14PC/C18PC to C14PC/C19PC) distinct breaks in the delta H versus c plots were observed. These mixtures displayed only one broad DSC endotherm. Mixtures of an unsaturated lipid C18: 1PC (dioleoyl) with C16PC or with C18PC showed two peaks, with each peak being associated with its parent lipid. However, the delta H versus c plots for each of these peaks showed an initial independence of cholesterol concentration followed by a dependence on cholesterol concentration. These results indicate that, in lipid mixtures, the type of interaction of cholesterol with each lipid component depends on the concentration of cholesterol present.     

Striking similarities between the regulatory mechanisms governing yeast mating-type genes and mammalian major histocompatibility complex genes.

Expression of a mammalian major histocompatibility complex (MHC) class I gene is in part regulated by a silencer DNA sequence element which binds a complex of silencer factors. This negative regulatory system is shown to be strikingly similar to the yeast alpha 2 mating-type repression system. A moderate DNA sequence homology exists between the MHC class I silencer DNA element and the yeast alpha 2 operator. Mammalian silencer factors specifically bind to the yeast alpha 2 operator DNA and also specifically interact with a yeast alpha 2-binding protein. Furthermore, the alpha 2 operator functions as a silencer element in mammalian cells when placed upstream of a MHC class I promoter.     

The Saccharomyces cerevisiae MYO2 gene encodes an essential myosin for vectorial transport of vesicles

After the initiation of bud formation, cells of the yeast Saccharomyces cerevisiae direct new growth to the developing bud. We show here that this vectorial growth is facilitated by activity of the MYO2 gene. The wild-type MYO2 gene encodes an essential form of myosin composed of an NH2-terminal domain typical of the globular, actin-binding domain of other myosins. This NH2-terminal domain is linked by what appears to be a short alpha-helical domain to a novel COOH-terminal region. At the restrictive temperature the myo2-66 mutation does not impair DNA, RNA, or protein biosynthetic activity, but produces unbudded, enlarged cells. This phenotype suggests a defect in localization of cell growth. Measurements of cell size demonstrated that the continued development of initiated buds, as well as bud initiation itself, is inhibited. Bulk secretion continues in mutant cells, although secretory vesicles accumulate. The MYO2 myosin thus may function as the molecular motor to transport secretory vesicles along actin cables to the site of bud development.     

The genotoxicity of nitrilotriacetic acid (NTA) in a somatic mutation and recombination test in Drosophila melanogaster

The genotoxicity of a chelating agent, the trisodium salt of nitrilotriacetic acid (NTA), was assessed in a somatic mutation and recombination test (SMART) in Drosophila melanogaster employing the wing hair markers mwh and flr3. The experiments were performed in parallel in two different laboratories (Padua, Italy and Schwerzenbach, Switzerland). The effectively absorbed doses of NTA, which was administered by feeding to larvae, were determined by a sensitive method employing [3H]leucine which allowed individual consumption levels to be measured. The particular pattern of clone induction produced by this compound suggests that NTA is active in inducing mitotic recombination and possibly aneuploidy in somatic cells of Drosophila. This is discussed in relation to the data present in the literature regarding the genotoxicity of NTA in a variety of experimental systems.     

Extinction,reduction, stability and increase: The responses of checkerspot butterfly (Euphydryas) populations to the California drought

Summary The California drought of 1975–77 has been correlated with unusual size changes in populations of two species of Euphydryas butterflies. Several populations became extinct, some were dramatically reduced, others remained stable and at least one increased. These differences in population dynamic response are not concordant with predictions made earlier that populations with heavy density-dependent mortality should be more stable in the face of drought than unregulated populations. The different responses are related to the fine details of the relationships between the insects and their host plants, relationships which are variable between populations. Revised predictions are given in the light of better knowledge of the variability and complexity of these insect-host relationships. The diversity of responses underlines the dangers of generalizing about the ecology of a taxonomic species. The extinctions support the view that such events are frequent and significant in the biology of populations.     

Composition and Thermal Properties of Membrane Lipids in Cryptoendolithic Lichen Microbiota from Antarctica

In Antarctica there exists a cryptoendolithic microbiota which survives extremely low temperatures. Fatty acid analysis of the membrane phospholipids of this microbial community showed a predominance of polyunsaturated fatty acids. Artificial membranes made from the purified community phospholipids remained fluid to below −20°C and had unusual hydration properties.