Alternations in lipid membrane fluidity and the physical state of cell-surface sialic acid in zinc-deficient rat erythrocyte ghosts

Erythrocyte ghosts, prepared from the blood of rats fed zinc-deficient diets, were evaluated for membrane fluidity and surface sialic acid properties using spin-labeled probes and electron spin resonance (ESR) spectroscopy. These physical parameters of the erythrocyte ghosts from the zinc-deficient group were compared to those for erythrocyte ghosts obtained from ad libitum and pair fed controls consuming zinc-adequate diets. As the animals became progressively zinc deficient, the erythrocyte ghost membranes became more fluid than those from the control groups. In addition, the apparent rotational correlation time of Tempamine spin probes on surface sialic acid residues was smaller for the zinc deficient group, indicative of an increased rotational mobility of the spin label. These results suggest that zinc deficiency can have pronounced effects on the physical state of membrane bilayer lipids and cell surface carbohydrates and supports the view that many of the pathological signs of zinc deficiency are due to a general membrane defect.     

Isolation and characterisation of transposon-induced mutants of Erwinia carotovora subsp. atroseptica exhibiting reduced virulence

Summary The blackleg pathogen Erwinia carotovora subsp. atroseptica (Eca) causes an economically important disease of potatoes. We selected a genetically amenable Eca strain for the genetic analysis of virulence. Tn5 mutagenesis was used to generate nine mutants which exhibited reduced virulence (Rvi^-) of strain SCRI1043. Following physiological characterisation, mutants were divided into three classes: (1) auxotrophs; (2) extracellular enzyme mutants; and (3) a growth rate mutant. The isolation of these Rvi^- mutants has allowed us to consider some factors that affect Eca virulence.     

Water use efficiency and carbon isotope composition of plants in a cold desert environment

Summary The effects of the availabilities of water and nitrogen on water use efficiency (WUE) of plants were investigated in a sagebrush steppe. The four species studied wereArtemisia tridentata (shrub),Ceratoides lanata (suffrutescent shrub),Elymus lanceolatus (rhizomatous grass), andElymus elymoides (tussock grass). Water and nitrogen levels were manipulated in a two-by-two factorial design resulting in four treatments: control (no additions), added water, added nitrogen, and added water and nitrogen. One instantaneous and two long-term indicators of WUE were used to testa priori predictions of the ranking of WUE among treatments. The short-term indicator was the instantaneous ratio of assimilation to transpiration (A/E). The long-term measures were 1) the slope of the relationship between conductance to water vapor and maximum assimilation and 2) the carbon isotope composition (¹³C) of plant material. Additional water decreased WUE, whereas additional nitrogen increased WUE. For both A/E and ¹³C, the mean for added nitrogen alone was significantly greater than the mean for added water alone, and means for the control and added water and nitrogen fell in between. This ranking of WUE supported the hypothesis that both water and nitrogen limit plant gas exchange in this semiarid environment. The short- and long-term indicators were in agreement, providing evidence in support of theoretical models concerning the water cost of carbon assimilation.     

Purified maturation promoting factor phosphorylates pp60c-src at the sites phosphorylated during fibroblast mitosis

We have previously shown that overexpressed chicken pp60c-src has retarded mobility, novel serine/threonine phosphorylation, and enhanced kinase activity during NIH 3T3 cell mitosis. Here we show that novel mitotic phosphorylations occur at Thr 34, Thr 46, and Ser 72. The possibility, previously raised, that Ser 17 is dephosphorylated during mitosis is excluded. The phosphorylated sites lie in consensus sequences for phosphorylation by p34cdc2, the catalytic component of maturation promoting factor (MPF). Furthermore, highly purified MPF from metaphase-arrested Xenopus eggs phosphorylated both wild-type and kinase-defective pp60c-src at these sites. Altered phosphorylation alone is sufficient to account for the large retardation in mitotic pp60c-src electrophoretic mobility: phosphorylation of normal pp60c-src by MPF retarded mobility and dephosphorylation of mitotic pp60c-src restored normal mobility. These results suggest that pp60c-src is one of the targets for MPF action, which may account in part for the pleiotropic changes in protein phosphorylation and cellular architecture that occur during mitosis.     

Infectivity-deficient vesicular stomatitis virus produced in the presence of interferon has a functional virion core

Interferon induces two antiviral actions against vesicular stomatitis virus by (i) inhibiting viral protein synthesis which leads to a reduction in virion production, and (ii) producing progeny which are deficient in infectivity (VSVIF). At low or physiological concentrations of interferon, while the virion production was decreased by less than 10-fold, the virion infectivity yield was suppressed more than 1000-fold. The VSVIF was found to be deficient (quantitatively) in envelop glycoprotein G and protein M. Tryptic peptide mapping indicated that there was no detectable structural abnormality in the G, M, and N proteins of VSVIF. The virion cores, lacking only the envelop G protein, isolated from VSVIF and control VSV have essentially identical specific infectivity. This indicated that the virion proteins L, N, NS, and M, as well as viral RNA that make up the virion core, must be functionally normal, and the observed deficiency in G protein was likely to be the cause of the functional deficiency of the virion. Low concentrations of DEAE-dextran, which is known to partially overcome the virion's dependence on the G protein for adsorption to the cell during infection, were found to enhance the infectivity of VSVIF more than the control virion. These results together indicated that the loss of infectivity in the VSVIF was due to the deficiency of the surface glycoprotein G.     

Agarose gel electrophoresis in isozyme separation and visualization

Isozyme analysis of rodent-human somatic cell hybrids has been used frequently to detect specific human chromosomes. The majority of these isozyme systems employs starch gels, the use of which can be laborious when screening large numbers of cell lines. We describe the development of two procedures to detect the long arms of human chromosomes 1 and 2 in Chinese hamster-human cell hybrids by a rapid and reproducible method using 1-mm-thick agarose gels. Detection of human chromosome 1q was accomplished by screening for human fumarate hydratase activity, whose gene has been mapped to 1q42.1. Detection of chromosome 2q was performed by screening for the isozyme isocitrate dehydrogenase 1, which has been localized to 2q32-qter. These systems provide a basis for the further development of procedures for detecting chromosome-specific isozyme markers in agarose gels.     

Scanning motion,ocellar morphology and orientation mechanisms in the phototaxis of the nematode Mermis nigrescens

Summary The putative ocellus of Mermis females consists of a hollow cylinder of dense hemoglobin pigmentation located in the anterior tip. The exact location of the photoreceptive nerve endings, however, is unknown. During phototaxis a continual bending or scanning motion of the head (anterior 2 mm) causes the orientation of the tip to swing about the direction of the source. By turning off (shuttering) the light source whenever the tip orientation was to one side of the source direction, the average orientation of the base of the head, and eventually the body orientation, was caused to be biased about 28° to the opposite side. Because the shuttering was synchronized with the scanning motion, the scanning motion must be involved in the maintenance of orientation to light. The direction of the bias rules out a two-signal comparison mechanism of orientation and demonstrates that a deviation of the tip from the source direction must decrease, rather than increase, the illumination of the photoreceptors. These findings, and the ocellar morphology, require that the photoreceptors be located inside the hollow tube of pigmentation where they can be shadowed by the pigment during deviations of the tip. Focusing by the curved anterior end should cause a similar modulation of the illumination at this location. The occasional episodes of transverse phototaxis can be explained by the leakiness of the pigment walls to transverse illumination. Analysis of the motion of the anterior in the presence and absence of shuttering indicates that the orientation of the base of the head, due to the motion of the neck, is controlled by the signals generated during one or more cycles of the scanning motion of the head. The orientation may be regulated by the phase relationship between the photoreceptor signal and putative proprioceptive signals that indicate the bending in the head.     

Rejection of B16 melanoma induced by expression of a transfected major histocompatibility complex class I gene.

Transfection of a functional major histocompatibility complex class I gene into certain tumor cells, induced by oncogenic viruses or chemical carcinogens, can effectively abrogate their tumorigenic activity. Since experimentally induced tumors possess strong tumor-specific transplantation antigens, expression of cell surface class I antigens may present the tumor cells to appropriate immune effector cells. Most spontaneously arising tumors do not possess tumor-specific transplantation antigens, and their tumorigenicity may not be affected by the expression of a transfected class I gene. We demonstrate that the poorly immunogenic B16-BL6 melanoma can be rendered nontumorigenic in syngeneic mice by the expression of the class I H-2K antigen but not the class II I-A antigen. Furthermore, the poorly tumorigenic, class I-expressing B16-BL6-transfected cells can effectively immunize syngeneic C57BL/6 mice against the highly tumorigenic, class I-deficient B16-BL6 parental cells. Our success in experimentally manipulating the tumorigenicity of a spontaneously derived neoplasm offers hope for a potential modality for the effective treatment of human cancer.     

Visual anthropology and multivocal ethnography: A dialogical approach to Japanese preschool class size

Joseph Jay Tobin is Assistant Professor of Family Studies at The University of New Hampshire