Ethological Isolation,Sexual Behavior and Pheromones in the Fasciatus Species Group of the Lizard Genus Eumeces

Ethological isolation was found among North American members of the fasciatus species group of Eumeces. Ethological isolation was investigated by staging a series of interspecific and intraspecific heterosexual encounters. No male E. laticeps or E. fasciatus courted heterospecific females. In both species, males courted and copulated with conspecific females in a significantly higher frequency of trials than with heterospecific females. However, male E. inexpectatus courted females of all three species, courting conspecific females and female E. laticeps at similar frequencies, but female E. fasciatus at a significantly lower frequency. No females of any of the three species were sexually receptive to heterospecific males, but forced copulation occurred in two of nine courtships of female E. fasciatus by male E. inexpectatus. Thus, ethological isolation in the fasciatus group appears to be complete with the possible exception of occasional forced copulation between male E. inexpectatus and female E. fasciatus. Preliminary evidence on the role of chemical stimuli in maintaining ethological isolation was obtained from experiments involving interspecific transfers of female odors. Male E. inexpectatus courted female E. fasciatus labelled with the odor of female E. inexpectatus in a significantly greater proportion of trials than they courted such females lacking the conspecific female odor. In a similar experiment, male E. fasciatus did not court female E. inexpectatus even if the females bore odors of female fasciatus.     

Sex pheromones enable Drosophila males to discriminate between conspecific females from different laboratory stocks

Drosophila melanogaster males from Canton-S and Oregon-R stocks perform more courtship in response to virgin females from the stock other than their own. Pairs of Canton-S and Oregon-R males also court each other more in the presence of volatile compounds extracted from Oregon-R and Canton-S females, respectively. These observations suggest that D. melanogaster females are polymorphic with respect to some components of their sex pheromone system and that males are capable of distinguishing females from their own stock and females from another stock on the basis of these differences in pheromone production.     

Assembly of the Yeast Vacuolar Proton-Translocating ATPase

The yeast vacuolar proton-translocating ATPase (V-ATPase) is the bestcharacterized member of the V-ATPase family. Biochemical and genetic screensled to the identification of a large number of genes in yeast, designatedVMA, encoding proteins required to assemble a functional V-ATPase. Atotal of thirteen genes encode subunits of the final enzyme complex. Inaddition to subunit-encoding genes, we have identified three genes that codefor proteins that are not part of the final V-ATPase complex yet required forits assembly. We refer to these nonsubunit Vma proteins as assembly factors,since their function is dedicated to assembling the V-ATPase. The assemblyfactors, Vma12p, Vma21p, and Vma22p are localized to the endoplasmicreticulum (ER) and aid the assembly of newly synthesized V-ATPase subunitsthat are translocated into the ER membrane. At least two of these proteins,Vma12p and Vma22p, function together in an assembly complex and interactdirectly with nascent V-ATPase subunits.     

Pseudomonas fluorescens subsp. cellulosa: an alternative model for bacterial cellulase

G.P. HAZLEWOOD, J.I. LAURIE, L.M.A. FERREIRA AND H.J. GILBERT. 1992. Pseudomonas fluorescens subsp. cellulosa , a Gram-negative soil bacterium, can utilize crystalline cellulose or xylan as main sources of carbon and energy. Synthesis of endoglucanases and xylanases is induced by Avicel, filter paper, carboxymethylcellulose or xylan and is repressed by cellobiose, glucose or xylose. These enzymes are secreted into the culture supernatant fluid and do not form aggregates or associate with the cell surface. Cells of Ps. fluorescens subsp. cellulosa do not adhere to cellulose. In cultures containing Avicel or filter paper, a significant proportion of the secreted cellulase and xylanase activities becomes tightly bound to the insoluble cellulose. Western blotting has revealed that endoglucanase B, xylanase A and a cellodextrinase encoded by genes previously isolated from Ps. fluorescens subsp. cellulosa and expressed in Escherichia coli , are synthesized by the pseudomonad under a variety of conditions. These enzymes appear to be post-translationally modified, probably through glycosylation. Overall, it appears that the cellulase/hemicellulase system of Ps. fluorescens subsp. cellulosa differs from the model established for celluloytic anaerobes such as Clostridium thermocellum.     

A New Family of Retroviral Long Terminal Repeat Elements in the Human Genome Identified by Their Homologies to an Element 5′ to the Spider Monkey Haptoglobin Gene

A new family of retroviral long terminal repeats that we name Spm-LTR has been identified as a result of DNA sequence comparisons between the entire GenBank databank and an element, SPHP, located 5′ to the haptoglobin gene of spider monkeys. The 18 human Spm-LTR sequences so identified fall into three subtypes. There is no sequence similarity between Spm-LTR elements and any endogenous retroviral LTR sequences previously reported except for general features that define LTRs. However, a previously described repeated sequence (MER-4) forms a portion of the Spm-LTR sequence.     

Phytoplankton cell size and the development of microenvironments

Abstract The effect of cell size on the development of extracellular microenvironments of pH produced by individual photosynthesizing phytoplankton cells was investigated. The presence of pH microenvironments was determined by detection of a chemical reaction known to occur in microenvironments of high pH produced by algal photosynthesis, specifically the extracellular oxidation of Mn(II) to MnO_x. The dye leukoberbelin blue was used to detect the reaction. It was experimentally determined that individual algal cells larger than 20 μm (length and/or width) produced microenvironments, while smaller cells did not unless present as cell aggregates larger than 20 μm. A mathematical model is presented and discussed.     

Nervous system modification by transplants and gene transfer

New possibilities to modify function and direct repair in the central nervous system (CNS) have been established by the merger of gene transfer technology with neural transplantation. Rapid advances in viral-mediated DNA-delivery procedures permit the study of novel gene expression in neurons and glial cells. Foreign genes, transferred by a virus vector, can be used to generate new cell lines, identify transplanted cells, and express growth factors or enzymes for neurotransmitter synthesis. In addition to CNS cell types, non-neural cells are also being studied with transgene technology in the nervous system. Functional effects have been obtained with grafts of genetically modified cells in animal models of several nervous system disorders, and the recent results set the stage for potential application of these techniques to human CNS gene therapy.     

Short-term UV-B radiation and ozone exposure effects on aromatic secondary metabolite accumulation and shoot growth of flavonoid-deficient Arabidopsis mutants

The presence of UV-absorptive substances in the epidermal cells of leaves is thought to protect mesophyll tissues from the harmful effects of UV-B radiation. We examined the influence of short-term UV-B exposures on UV-absorptive (330 nm) sinapates and flavonols, and on shoot growth of the Arabidopsis wild type ecotype Landsberg erecta and two mutants. 114 deficient in chalcone synthase, and 115 , deficient in chalcone/flavonone isomerase. Sequential ozone exposures were used to determine the effects of oxidative stress The levels of sinapates and flavonols on a leaf fresh weight basis increased substantially in the wild type and sinapates increased in the 114 mutant in vegetative vegetative/reproductive transitional and reproductive stage plants in response to short-term (48h) UV-B radiation. When UV-B was discontinued the levels generally decreased lo pre-exposure levels after 48 h in vegetative/reproductive but not in reproductive plants. Exposure to ozone before or alter UV-B treatment did not consistently affect the levels of these UV-absorptive compounds. Dry matter accumulation was less affected by UV-B at the vegetative and reproductive stages than at the vegetative/reproductive stage. At the vegetative/reproductive stage, shoot growth of all 3 genotypes was retarded by UV-B. Growth was not retarded by short-term ozone exposure alone but when exposure to ozone followed UV-B exposure, growth was reduced in all genotypes. Leaf cupping appeared on 115 plants exposed to UV-B.