Behaviorial evolution: does similarity breed cooperation?

Reciprocity, whether direct or indirect, is thought to be the key to establishing cooperation among non-relatives. But Riolo et al. have presented a model in which cooperation is instead based on similarity: agents donate only when their partner's 'tag' lies within a 'tolerance' range around their own. Here we point out that their model requires individuals with identical tags to cooperate with each other, and show that cooperation tends to collapse when individuals bearing identical tags are given the option of not donating. We therefore question their mechanism for maintaining cooperation without reciprocity.     

A mouse knock-in model exposes sequential proteolytic pathways that regulate p27Kip1 in G1 and S phase

The protein p27Kip1 is an inhibitor of cell division. An increase in p27 causes proliferating cells to exit from the cell cycle, and a decrease in p27 is necessary for quiescent cells to resume division. Abnormally low amounts of p27 are associated with pathological states of excessive cell proliferation, especially cancers. In normal and tumour cells, p27 is regulated primarily at the level of translation and protein turnover. Phosphorylation of p27 on threonine 187 (T187) by cyclin-dependent kinase 2 (Cdk2) is thought to initiate the major pathway for p27 proteolysis. To critically test the importance of this pathway in vivo, we replaced the murine p27 gene with one that encoded alanine instead of threonine at position 187 (p27T187A). Here we show that cells expressing p27T187A were unable to downregulate p27 during the S and G2 phases of the cell cycle, but that this had a surprisingly modest effect on cell proliferation both in vitro and in vivo. Our efforts to explain this unexpected result led to the discovery of a second proteolytic pathway for controlling p27, one that is activated by mitogens and degrades p27 exclusively during G1.     

Human transforming growth factor-beta complementary DNA sequence and expression in normal and transformed cells

The partial amino-acid sequence of purified human transforming growth factor-beta (TGF-beta) was used to identify a series of cDNA clones encoding the protein. The cDNA sequence indicates that the 112-amino acid monomeric form of the natural TGF-beta homodimer is derived proteolytically from a much longer precursor polypeptide which may be secreted. TGF-beta messenger RNA is synthesized in various normal and transformed cells.     

Testing cumulative prediction errors in event study methodology

This paper reconsiders event study methodology, a very popular technique in the applied finance literature, within the context of testing cumulative prediction errors. It extends the conventional test statistics in two directions. First, it accounts fully for the increased variance of prediction errors outside of the estimation period and for the cumulation of these errors across different event windows. Second, it also takes account of the fact that market model residuals are typically serially correlated, heteroscedastic and non-normal. The statistics are compared with the conventional approach by reassessing a previous application of the methodology to the impact of management buyouts.     

Different antiviral spectra of human macrophage interferon activities

The antiviral activity of alpha-interferon (IFN-alpha) produced by human leukocytes in response to viral infection has been considered to be independent of the virus which induced its production. Recently, however, IFN-alpha has been found to include at least eight different subtypes, as indicated by measurement of antigenic variability, DNA hybridization and amino acid sequencing. We considered the possibility that interferon heterogeneity may play a part in enhancing host antiviral defence and now present data suggesting that purified human macrophages, when exposed to different viruses, produce interferons having differing spectra of antiviral activity. These findings may provide a functional correlation for IFN-alpha heterogeneity.     

E. coli recA protein-directed cleavage of phage lambda repressor requires polynucleotide

The recA protein mediates both genetic recombination and several cellular responses to DNA damage, including the induction of temperate bacteriophage. Indication of phage lambda results from proteolytic cleavage of lambda repressor directed by recA protein. We show here that this cleavage reaction requires both polynucleotide and ATP. We suggest that a stoichiometric complex of recA protein and DNA is active both to destroy repressors by proteolytic cleavage and to initiate pairing of this DNA to its homologous sequence in a DNA duplex ('strand invasion').     

基于遗传粒子滤波的轮毂驱动电动汽车质心侧偏角估计方法

质心侧偏角估计是汽车稳定性控制系统中的关键技术.为了解决现有估计方法对轮毂驱动电动汽车信息利用不充分、估计精度低的问题,提出一种基于遗传粒子滤波(GPF)的轮毂驱动电动汽车质心侧偏角估计方法.利用魔术轮胎公式,融合轮毂驱动电动汽车车轮上驱动与制动力矩信息,建立非线性车辆动力学模型,实现轮胎纵向力与侧向力计算,完成质心侧偏角估计器的搭建.针对车辆动力学模型的强非线性及传统粒子滤波算法粒子退化、计算量大的问题,设计适用于强非线性系统并且能够有效抑制退化、减小计算量的遗传粒子滤波算法对质心侧偏角进行估计.仿真结果表明:所提出的估计方法能够提高质心侧偏角的估计精度和鲁棒性.