Accumulation of independent cultural traits

In a species capable of (imperfect) social learning, how much culture can a population of a given size carry? And what is the relationship between the individual and the population? In the first study of these novel questions, here we develop a mathematical model of the accumulation of independent cultural traits in a finite population with overlapping generations.     

Sublocalization of a locus at 3p21.3–23 predisposing to hereditary nonpolyposis colon cancer

Hereditary nonpolyposis colon cancer (HNPCC) is a heterogeneous disease caused by at least three different genes on chromosomes 2 and 3, and one or more additional chromosomes. We used 19 dinucleotide markers in order to sublocalize further the 3p locus linked to HNPCC, and to order the markers into one map resulting in a panel of markers suitable for linkage studies. Human chromosome 3 mouse hybrids were used to determine the chromosomal position of the markers. Haplotype analysis in two families where the disease is linked to chromosome 3p21–23 was used in order to sublocalize further the region in which the gene is located. Based on our results, the gene has now been localized to the region 3p21.3–23.     

Effect of sterol structure on the bending rigidity of lipid membranes: A H NMR transverse relaxation study

The effect of incorporation of 3-43 mol% sterol on the lipid order and bilayer rigidity has been investigated for model membranes of dimyristoylphosphatidylcholine or dipalmitoylphosphatidylcholine. ²H NMR spectra and spin-lattice relaxation rates were measured for macroscopically aligned bilayers. The characteristics of spectra obtained at temperatures between 0-60 °C are interpreted in terms of a two-phase coexistence of the liquid disordered and the liquid ordered phases and the data is found to be in agreement with the phase diagram published by Vist and Davis (Biochemistry 29 (1990), pp. 451-464). The bending modulus of the bilayers was calculated from plots of relaxation rate vs. the square of the order parameter at 44 °C. Clear differences were obtained in the efficiency of the sterols to increase the stiffness of the bilayers. These differences are correlated to the ability of the sterols to induce the liquid ordered phase in binary as well as in ternary systems; the only exception being ergosterol, which was found to be unable to induce l_o phases and also had a relatively weak effect on the bilayer stiffness in contrast to earlier reports.     

Enzymatic RNA reduction in disintegrated cells of Saccharomyces cerevisiae

Degradation of UNA by endogenous RNase in cell suspensions of Saccharomyces cerevisiae was found to be achieved by mechanical disintegration followed by incubation in the presence of NaCl. The incubation parameters pH, temperature, time, and concentration of NaCl were investigated. Protein concentrates with a low content of RNA were obtained by precipitation of the incubated suspensions and separation of the degradation products. On a pilot plant scale the incubation was performed at 50°C and pH 5.6 in the presence of 3% NaCl for 20 min. Kilogram quantities of protein concentrates containing 1.4% RNA and 8.2% nitrogen were obtained. The RNA reduction and the nitrogen yield was 85 and 60%, respectively. The yield of amino acids was about 75%. The process described can probably be applied for large-scale production.     

The Origins and Maintenance of Female Genital Modification across Africa

We present formal evolutionary models for the origins and persistence of the practice of Female Genital Modification (FGMo). We then test the implications of these models using normative cross-cultural data on FGMo in Africa and Bayesian phylogenetic methods that explicitly model adaptive evolution. Empirical evidence provides some support for the findings of our evolutionary models that the de novo origins of the FGMo practice should be associated with social stratification, and that social stratification should place selective pressures on the adoption of FGMo; these results, however, are tempered by the finding that FGMo has arisen in many cultures that have no social stratification, and that forces operating orthogonally to stratification appear to play a more important role in the cross-cultural distribution of FGMo. To explain these cases, one must consider cultural evolutionary explanations in conjunction with behavioral ecological ones. We conclude with a discussion of the implications of our study for policies designed to end the practice of FGMo.     

Membrane Interaction of the Glycosyltransferase WaaG

The glycosyltransferase WaaG is involved in the synthesis of lipopolysaccharides that constitute the outer leaflet of the outer membrane in Gram-negative bacteria such as Escherichia coli. WaaG has been identified as a potential antibiotic target, and inhibitor scaffolds have previously been investigated. WaaG is located at the cytosolic side of the inner membrane, where the enzyme catalyzes the transfer of the first outer-core glucose to the inner core of nascent lipopolysaccharides. Here, we characterized the binding of WaaG to membrane models designed to mimic the inner membrane of E. coli. Based on the crystal structure, we identified an exposed and largely α-helical 30-residue sequence, with a net positive charge and several aromatic amino acids, as a putative membrane-interacting region of WaaG (MIR-WaaG). We studied the peptide corresponding to this sequence, along with its bilayer interactions, using circular dichroism, fluorescence quenching, fluorescence anisotropy, and NMR. In the presence of dodecylphosphocholine, MIR-WaaG was observed to adopt a three-dimensional structure remarkably similar to the segment in the crystal structure. We found that the membrane interaction of WaaG is conferred at least in part by MIR-WaaG and that electrostatic interactions play a key role in binding. Moreover, we propose a mechanism of anchoring WaaG to the inner membrane of E. coli, where the central part of MIR-WaaG inserts into one leaflet of the bilayer. In this model, electrostatic interactions as well as surface-exposed Tyr residues bind WaaG to the membrane.