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.      

Brain myelin-bound Zn2+-glycerophosphocholine cholinephosphodiesterase is a glycosylphosphatidylinositol-anchored enzyme of two different molecular forms

A Zn²⁺-GPC cholinephosphodiesterase activity, which is present more predominently in myelin than in microsome or cytosol, has been examined using -nitrophenylphosphocholine as a substrate. In the solubilization of enzyme activity from myelin membranes, lysolecithin was found to be more effective than Triton X-100 or deoxycholate. Especially, the myelin-bound phosphodiesterase was suggested to be a glycosylphosphatidyl-inositol-anchored protein, based on solubilization by B. cereus phospholipase C and Triton X-114 phase separation. Interestingly, it was found that while phospholipase C-solubilized enzyme, a hydrophilic protein, was associable with Concanavalin A column, detergent-solubilized amphiphilic form of enzyme was not. Either detergent extract or cytosol was observed to contain both amphiphilic form and hydrophilic one. In CM-sephadex chromatography, the soluble hydrophilic phosphodiesterase was observed to be separatable into two forms of enzyme. In comparative studies, both forms of phosphodiesterase showed much similarity in substrate specificity, optimum pH, Km value and Zn²⁺ requirement, although they differed in charge property and molecular weight.     

Peptic ulceration,gastric secretion,and renal transplantation.

Fifty-four patients on haemodialysis for chronic renal failure underwent renal transplantation. Basal and maximum acid output and the incidence of peptic ulcer before transplantation were not significantly different from those of controls. But after renal transplantation the incidence of symptoms of peptic ulcer was high (22%) and four out of six patients who developed gastrointestinal bleeding died from this complication. In men peak acid output was significantly increased after renal transplantation and was associated with a 30% incidence of symptoms of peptic ulcer compared with 10% in women, who showed no significant change in mean basal or peak acid output. Peptic ulceration after transplantation was not associated with steroid dosage, hyperparathyroidism, or the height of blood urea concentrations. Given criteria of a history of dyspepsia, abnormal barium meal findings, or gastric hypersecretion, it was not possible to identify patients at risk from peptic ulceration or life-threatening complications after renal transplantation. Thus the routine screening of these patients for peptic ulcer has no practical value, and the incidence of fatal complications is not high enough to justify routine prophylactic anti-ulcer surgery aimed at reducing acid secretion before renal transplantation.     

Reaction of ethanol radicals with ribonuclease.

Ribonuclease was irradiated under conditions such that ethanol radicals were the main reactive species in solution. Sephadex gel filtration of the irradiated solution demonstrated that ethanol radicals had reacted with the ribonuclease and had become firmly bound to the enzyme molecule. The number of ethanol molecules bound to ribonuclease was a function of dose and correlated with the loss of enzymatic activity and with the changes in the molecular configuration of the enzyme molecule.     

Survival of Salmonella adelaide and fecal coliforms in coarse sands of the swan costal plain, Western Australia.

The survival of Salmonella adelaide and fecal coliforms in two coarse sands influenced by two sources of septic tank effluent was studied. The experiments were conducted in conditions that reflected the soil environment beneath functioning septic tank systems. Significant differences in survival were found with different effluent sources. In one experiment the survival of S. adelaide was similar to that of fecal coliforms; in the other it was not. The nonuniform, multiphasic nature of survival curves was variability observed in these experiments suggests that the application of such survival data for establishing management criteria for septic tank systems--by, for example, the use of soil moisture characteristic curves to give estimates of movement in the soil--is inappropriate.     

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.     

Solution structure of the cytoplasmic domain of human CD99 type I

Human CD99, which is encoded by the mic2 gene, is a ubiquitous 32 kDa transmembrane protein. Its major cellular functions are related to homotypic cell adhesion, apoptosis, vesicular protein transport, and differentiation of thymocytes or T cells. Recent reports have suggested that expression of a splice variant of CD99 increases the invasiveness of human breast cancer cells. In order to determine the structural basis of CD99 function, we have initiated structural studies on the human CD99 Type I cytoplasmic domain (hCD99cytoI) using circular dichroism and multi-dimensional NMR spectroscopy. The solution structure of hCD99cytoI shows that it has a hairpin shape anchored by two flexible loops. Consequently, hCD99cytoI does not have any regular secondary structural element; however, the NMR and CD data indicate that it possesses an intrinsic helical nature.     

Test of pangamy by genetic analysis of Schistosoma mansoni pairs within its natural murine host in Guadeloupe

Mating system plays a determinant role in the maintenance and distribution of genetic variations. It can be assessed indirectly by analyzing the distribution of the genetic variability within populations or directly by considering how mating pairs are formed. In the present study, 71 pairs of adult Schistosoma mansoni worms sampled from naturally infected rats were genotyped to investigate how male and female schistosomes paired according to their genetic relatedness. Among all samples, pangamy, the random association between males and females, could not be rejected. Whereas the schistosome mating system has been intensively studied under experimental conditions, to the best of our knowledge, our study is the first to attempt to understand the way in which males and females pair in natural conditions.