Effects of increasing the number of players and memory size in the iterated Prisoner's Dilemma: a numerical approach

The Prisoner''s Dilemma has become a paradigm for the evolution of altruistic behaviour. Here we present results of numerical simulations of the infinitely iterated stochastic simultaneous Prisoner''s Dilemma considering players with longer memory, encounters of more than two players as well as different pay-off values. This provides us with a better foundation to compare theoretical results to experimental data. We show that the success of the strategy Pavlov, regardless of its simplicity, is far more general by having an outstanding role in the iterated N-player N-memory Prisoner''s Dilemma. Besides, we study influences of increased memory sizes in the iterated two-player Prisoner''s Dilemma, and present comparisons to results of experiments with first-year students.     

Random selection—A simple model based on linear birth and death processes

Linear birth and death processes are used to derive simple expressions for sequential extinction times and gene fixation probabilities in asexual populations.     

Studies on the mechanism of assembly of tobacco mosaic virus.

Sedimentation and proton binding studies on the endothermic self-association of tobacco mosaic virus (TMV) protein indicate that the so-called "20S" sedimenting protein is an interaction system involving at least the 34-subunit two-turn yield cylindrical disk aggregate and the 49-subunit three-turn helical rod. The pH dependence of this overall equilibrium suggests that disk formation is proton-linked through the binding of protons to the two-turn helix which is not present as significant concentrations near pH 7. There is a temperature-induced intramolecular conformation change in the protein leading to a difference spectrum which is complete in 5 x 10(-6) s at pH 7 and 20 degrees C and is dominated at 300 nm by tryptophan residues. Kinetics measurements of protein polymerization, from 10(-6) to 10(3) s, reveal three relaxation processes at pH 7.0, 20 degrees C, 0.10 M ionic strength K (H) PO4. The fastest relaxation time is a few milliseconds and represents reactions within the 4S protein distribution. The second fastest relaxation is 50-100 x 10(-3) s and represents elementary polymerization steps involved in the formation of the approximately 20 S protein. Analysis of the slowest relaxation, approximately 5 x 10(4) s, suggests that this very slow formation of approximately 20 S protein may be dominated by some first order process in the overall dissociation of approximately 20S protein. Sedimentation measurements of the rate of TMV reconstitution, under the same conditions, show by direct measurements of 4S and approximately 20S incorporation at various 4S to approximately 20S weight ratios that the relative rate of approximately 20S incorporation decreases almost linearly, from 0 to 50% 4S. There appears to be one or more regions of TMV-RNA, approximately 1-1.5 kilobases long, which incorporates approximately 20S protein exclusively. Solutions of approximately 95-100% approximately 20S protein have been prepared for the first time and used for reconstitution with RNA. Such protein solutions yield full size TMV, but at a slower rate than if 4S protein is added. Thus the elongation reaction in TMV assembly, following nucleation with approximately 20S protein, is not exclusively dependent upon the presence of either 4S or approximately 20S protein aggregates. The initial, maximum, rate of reconstitution increases about threefold when the protein composition is changed from 5% to 30% 4S protein, at constant total protein concentration at pH 7.0, 20 degrees C in 0.10 M ionic strength K (H)PO4. The probable binding frame at the internal assembly nucleation site of TMV-RNA has been determined by measuring the association constants for the binding of various trinucleoside diphosphates to helical TMV protein rods. The -CAG-AAG-AAG-sequence at the nucleation site is capable of providing at least 10-14 kcal/mol of sites of binding free energy for the nucleation event in TMV self-assembly.     

Insecticidal activity ofBacillus thuringiensis strains against the egyptian cotton leaf wormSpodoptera littoralis [Lep.: Nocutidae]

Among more than 50 isolates ofBacillus thuringiensis Berliner (B.t.) tested, 7 incited 100% mortality when 2nd instar larvae ofSpodoptera littoralis Boisduval were fed on alfalfa leaves dipped in a spore-crystal suspension of 10⁸ colony forming units/ml. Among those isolates,B.t. 24 demonstrated the highest activity. Larvae of instars 1 and 2 were the most susceptible toB.t. Susceptibility decreased with larval development. However, larvae of all instars were killed by isolateB.t. 24. Larvae that survived after feeding withB.t. 24 were retarded and fed less. Their weight relative to the controls was lower as the spore concentration on the leaves on which they fed was higher. Survival of the spores in the field dropped drastically to 2% after 4 days. Insecticidal activity of the sprayed suspension on those leaves, however, remained significant.B.t. 24 was also effective against larvae on cotton plants in the greenhouse and in a preliminary field experiment. Numbers of colony forming units recovered from leaves dipped in suspension of various spore concentrations showed significant correlation with the initial concentrations as did sprayed leaves. However, colony forming units recovered from sprayed leaves were 5–7.5 fold lower than from dipped leaves. Dipped cotton leaves showed 3.1×10^?5 ml attached to 1 mm² leaf surface whereas sprayed ones had 6×10^?6 ml. Those data are important for the determination of spore concentrations in suspensions required for spraying. The isolateB.t. 24 was serotyped byH. de Barjac as H-6B. thuringiensis entomocidus.     

Escherichia coli dnaB protein. Affinity chromatography on immobilized nucleotides.

The purification of the Escherichia coli dnaB protein by affinity chromatography on nucleotides bound to agarose is described. The dnaB protein, which contains an associated ribonucleoside triphosphatase activity (Wickner, S., Wright, M., and Hurwitz, J. (1974) Proc. Natl. Acad. Sci. U. S. A. 71, 783-787) binds to immobilized ATP, ADP, and UDP, but not to AMP. The type of linkage of ATP to agarose influences the adsorption, elution, and purification of the enzyme. Optimal purification is achieved using ATP bound to agarose via its oxidized ribose moiety. By this means, the dnaB protein can be obtained at least 95% electrophoretically pure after only three purification steps. The enzyme can be eluted from immobilized nucleoside-5'-di- and -triphosphates by ATP, ADP, and pyrophosphate, but not by AMP or orthophosphate. ADP and pyrophosphate, as well as the substrate ATP in high concentration are at the same time inhibitors of the ribonucleoside triphosphatase. The dnaB complementing and ribonucleoside triphosphatase activities could not be separated from each other by affinity chromatography, supporting the finding of others that they both reside on the same protein complex, namely a dnaB multimer. The results indicate that the dnaB protein binds to immobilized nucleotides by means of its ribonucleoside triphosphatase, and that at least the pyrophosphate moiety is essential for adsorption as well as elution of the enzyme.     

Verstärkung der antiphytoviralen Wirkung von 2,4-Dioxohexahydro-l,3,5-triazin durch Kombination mit Verbindungen mit Guanidinstruktur

Intensified antiphytoviral activity of 2,4-dioxohexahydro-l,3,5-triazine by combination with guanidines Combined application of the antiphytoviral compound 2,4-dioxohexahydro-l,3,5 triazine (DHT) and different guanidines (GDs) that were either unsubstituted or substituted only by low-molecular substituents reduced the concentration of potato virus χ (PVX) in leaves or Nicotiana tabacum L. cv. Samsun much more than application of either agent alone. In secondarily PVX-infected leaves, the activity of 2,4-dioxohexahydro- 1,3,5-triazine was increased by a larger number of GDs and to a greater degree than in inoculated ones. The activities of GDs against tobacco mosaic virus (TMV) in Nicotiana tabacum L. cv. Samsun as well as against brome grass mosaic virus (BRV) in Hordeum vulgare L. cv Vogelsanger Gold were only insignificantly increased by combination with DHT. On the other hand, in experiments with so-called identical potato eye cuttings, in which several eye cuttings were obtained from each potato tuber, one serving as a control and the others being treated with DHT, N-cyano guanidine or a combination of these substances, the number of cuttings with symptoms of potato leaf-roll virus (PLRV) could be much more greatly reduced by the combination than by the individual preparations. The number of cuttings with symptoms of potato virus Y and potato virus A was significantly reduced by treatment with the combined preparation, but not by treatment with DHT or N-cyano guanidine alone. Additional investigation with N-cyano-GD, and, beside this, with acetyl-GD and N N′ N triamino-GD indicated a close correlation between the diminution of numbers of potato eye cuttings with virus symptoms and the increase in tuber weight. The greater the reduction in the number of cuttings showing virus symptoms, the greater was the increase in tuber weight. These relationships were observed even in those cases where controls had been treated with ammonium nitrate solutions whose N contents equivalent to the N contents of the preparations. The observed effects of the preparations therefore are not attributable to N-fertilizing effects.     

Structural requirements for nucleophilic substrates of carboxypeptidase Y

The composition and structural aspects of the amino and carboxylic acid groups required for incorporation into peptides by transpeptidation and inhibition of hydrolysis in carboxypeptidase Y-catalyzed reactions were studied. Separation of these two groups by even one carbon prevents incorporation by transpeptidation and does not inhibit incorporation of other amino acids into model peptides. Substitution of phosphonic or sulfonic acids for the carboxylic acid group also results in loss of incorporation by transpeptidation. Only the sulfonic acid analog of glycine causes inhibition of hydrolysis and this inhibition is lost when serine is included in the reaction. d-Serine is not incorporated by carboxypeptidase Y, and its presence in the reaction mixture does not inhibit the incorporation of the L-isomer.     

Breast reconstruction in women treated with radiation therapy for breast cancer: cosmesis, complications, and tumor control.

The records of 55 patients who had breast cancer treated by mastectomy, irradiation, and breast reconstruction were reviewed for cosmetic outcome, complications, and tumor control. Median follow-up was 35 months. Local control rates were 95 percent in patients treated for high risk factors or breast conservation and 85 percent in patients treated for recurrent breast cancer. Acceptable cosmetic results were obtained in only 42 percent of patients. The incidence of complications was 55 percent. Transverse rectus abdominis muscle (TRAM) reconstructions gave superior cosmetic results compared with all other types of reconstructions. The timing of reconstruction in relation to mastectomy or radiation therapy did not significantly influence cosmetic outcome, although other factors suggest that delayed reconstruction may give better results. A majority of patients were satisfied with cosmetic outcome.     

Sequence alignment of the G-protein coupled receptor superfamily.

The multitude of G-protein coupled receptor (GPR) superfamily cDNAs recently isolated has exceeded the number of receptor subtypes anticipated by pharmacological studies. Analysis of the sequence similarities and unique features of the members of this family is valuable for designing strategies to isolate related cDNAs, for developing hypotheses concerning substrate-ligand and receptor-effector interactions, and for understanding the evolution of these genes. We have compiled and aligned the 74 unique amino acid sequences published to date and review the present understanding of the structural motifs contributing to ligand binding and G-protein coupling.