Multiple duplications of yeast hexose transport genes in response to selection in a glucose-limited environment

When microbes evolve in a continuous, nutrient-limited environment, natural selection can be predicted to favor genetic changes that give cells greater access to limiting substrate. We analyzed a population of baker's yeast that underwent 450 generations of glucose-limited growth. Relative to the strain used as the inoculum, the predominant cell type at the end of this experiment sustains growth at significantly lower steady-state glucose concentrations and demonstrates markedly enhanced cell yield per mole glucose, significantly enhanced high-affinity glucose transport, and greater relative fitness in pairwise competition. These changes are correlated with increased levels of mRNA hybridizing to probe generated from the hexose transport locus HXT6. Further analysis of the evolved strain reveals the existence of multiple tandem duplications involving two highly similar, high- affinity hexose transport loci, HXT6 and HXT7. Selection appears to have favored changes that result in the formation of more than three chimeric genes derived from the upstream promoter of the HXT7 gene and the coding sequence of HXT6. We propose a genetic mechanism to account for these changes and speculate as to their adaptive significance in the context of gene duplication as a common response of microorganisms to nutrient limitation.      

Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands

The alpha3 fucosyltransferase, FucT-VII, is one of the key glycosyltransferases involved in the biosynthesis of the sialyl Lewis X (sLex) antigen on human leukocytes. The sialyl Lewis X antigen (NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential component of the recruitment of leukocytes to sites of inflammation, mediating the primary interaction between circulating leukocytes and activated endothelium. In order to characterize the enzymatic properties of the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been expressed in Trichoplusia ni insect cells. The enzyme is capable of synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from 3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies using fucosylated NeuAcalpha(2-3)-(Galbeta(1- 4)GlcNAc)3-Me acceptors demonstrate that FucT-VII is able to synthesize both di-fucosylated and tri-fucosylated structures from mono- fucosylated precursors, but preferentially fucosylates the distal GlcNAc within a polylactosamine chain. Furthermore, the rate of fucosylation of the internal GlcNAc residues is reduced once fucose has been added to the distal GlcNAc. These results indicate that FucT-VII is capable of generating complex selectin ligands, in vitro , however the order of fucose addition to the lactosamine chain affects the rate of selectin ligand synthesis.      

Plankton size distributions and trophic relations before and after the construction of the storm-surge barrier in the Oosterschelde estuary

Phytoplankton and zooplankton biomass distributions were calculated on a carbon basis for the inland part of the Oosterschelde, in the period before (1983), during (1984, 1986) and after (1987, 1988) the construction of the storm- surge barrier. In all years studied, both phytoplankton and zooplankton distributions are very irregular, and little consistent patterns emerge. The data were used to test the model of Sheldon et al. (1977). The observed standing stock ratios of zooplankton to phytoplankton agree with the model predictions in 1983, and are slightly higher during the period 1984–1987. In 1988, the model predictions are very different from the observed values, because of important changes in the zooplankton species abundance occurring in this year.     

Identification of the catalytic and DNA-binding region of the human immunodeficiency virus type I integrase protein.

The integrase (IN) protein of the human immunodeficiency virus (HIV) is required for specific cleavage of the viral DNA termini, and subsequent integration of the viral DNA into target DNA. To identify the various domains of the IN protein we generated a series of IN deletion mutants as fusions to maltose-binding protein (MBP). The deletion mutants were tested for their ability to bind DNA, to mediate site-specific cleavage of the viral DNA ends, and to carry out integration and disintegration reactions. We found that the DNA-binding region resides between amino acids 200 and 270 of the 288-residues HIV-1 IN protein. The catalytic domain of the protein was mapped between amino acids 50 and 194. For the specific activities of IN, cleavage of the viral DNA and integration, both the DNA-binding domain and the conserved amino-terminal region of IN are required. These regions are dispensable however, for disintegration activity.     

The human immunodeficiency virus integrase protein

The DNA integration step in the replication cycle of the human immunodeficiency virus (HIV) has been recognized as an important target in antiviral strategies. There are two main reasons for this. First, integration of HIV DNA into the human genome is required for replication of this retrovirus. Second, since the integration reaction does not have an obvious cellular counterpart, drugs that specifically inhibit integration may not be toxic for the cell. Here, we focus on the only protein known to be required for retroviral integration, the integrase (IN) protein.     

Studies on the response ofAmblyseius bibens [Acarina: Phytoseiidae] to conditions of prey scarcity

Various aspects of the ability of the predacious miteAmblyseius bibens Blommers to survive under conditions of prey scarcity were studied in the laboratory. The presence of water considerably lengthened survival in the absence of food. An ability to pierce leaves was not observed in the predator. Walking speed was little affected by hunger, but declined with inanition. Activity (=percentage time spent walking) was greatest in well fed females, and decreased with increasing hunger, and eventually with inanition. Hence, the area searched per unit time decreased with increasing hunger and inanition. Hungry predators showed greater activity on more hairy leaves. Hungry predators became more restive in the presence of a cover. A webbed area was preferred (as resting place) by the predator, whether hungry or not. Gut content, and hence initial feeding, was only representative for the state of hunger, if the availibility of water was accounted for. Duration of the complete recovery (oviposition) in the presence of ample food provided a measure of the original inanition. Many kinds of pollen might serve as alternate food.     

ERRATUM: New Body Mass Estimates for Omomys carteri,a Middle Eocene Primate From North America. Am J Phys Anthropol 109:41–52.

Payseur BA, Covert HA, Vinyard CJ, Dagosto M. 1999. New Body Mass Estimates for Omomys carteri, a Middle Eocene Primate From North America. Am J Phys Anthropol 109:41–52. This article included an incomplete Table 2. The final two columns, showing “Intercept” and “SEE” data were omitted. The complete Table 2, with these two columns included, is provided below.     

Capillary endothelial surface layer selectively reduces plasma solute distribution volume

We previously reported that a 0.4- to 0.5-microm-thick endothelial surface layer confines Dextran 70 (70 kDa) to the central core of hamster cremaster muscle capillaries. In the present study we used a variety of plasma tracers to probe the barrier properties of the endothelial surface layer using combined fluorescence and brightfield intravital microscopy. No permeation of the endothelial surface layer was observed for either neutral or anionic dextrans >/=70 kDa, but a neutral Dextran 40 (40 kDa) and neutral free dye (rhodamine, 0.4 kDa) equilibrated with the endothelial surface layer within 1 min. In contrast, small anionic tracers of similar size (0. 4-40 kDa) permeated the endothelial surface layer relatively slowly with half-times (tau(50)) between 11 and 60 min, depending on tracer size. Furthermore, two plasma proteins, fibrinogen (340 kDa) and albumin (67 kDa), moved slowly into the endothelial surface layer at the same rates, despite greatly differing sizes (tau(50) approximately 40 min). Dextran 70, which did not enter the glycocalyx over the course of these experiments, entered at the same rate as free albumin when it was conjugated to albumin. These findings demonstrate that for anionic molecules size and charge have a profound effect on the penetration rate into the glycocalyx. The equal rates of penetration of the glycocalyx demonstrated by the different protein molecules suggests that multiple factors may influence the penetration of the barrier, including molecular size, charge, and structure.     

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Corrigendum