Recognition and the evolution of distinctive signatures: when does it pay to reveal identity?

A simple evolutionarily stable strategy (ESS) model of identity advertisement is presented, which is applicable to many different situations, ranging from parental recognition of young to recognition of kin by workers in social insect colonies that comprise several genetically distinct lineages. The model assumes that the receiver may respond favourably or unfavourably to the signaller, but that it cannot immediately determine which type of response is appropriate. The signaller, who always benefits by eliciting a favourable response (but is unaware of which type of response is appropriate for the receiver), may choose to reveal or conceal its identity, making the task of discrimination easier or harder for the receiver. The evolutionarily stable outcome of the model depends on the probability that an unfavourable response is appropriate, the relative costs to the receiver of acceptance and rejection errors, and the relative benefits to the signaller of eliciting a favourable response when this is appropriate and when it is inappropriate for the receiver. High costs of acceptance errors to the receiver, and high benefits of appropriate favourable responses to the signaller, favour provision of distinctive identity cues: so, paradoxically, does a high probability that an unfavourable response is appropriate. However, under a wide range of conditions, selection favours the withholding of signature cues, which prevents discrimination by the receiver. Finally, if the signaller must provide some information to elicit a favourable response, but stands to gain more from such a response when it is undesirable, it may do best to provide partial but incomplete information about its identity.     

Schooling preferences for familiar fish vary with group size in a wild guppy population

The ability of fish to recognize and preferentially associate with familiar conspecifics has been well documented in a series of laboratory experiments. In this paper we investigate the schooling preferences of wild female guppies, Poecilia reticulata, in the Upper Tunapuna River in Trinidad and confirm that they do indeed prefer to associate with familiar individuals. The guppies in this river occur in a series of pools that become isolated during the dry season. These fish interact solely with other individuals in their pool for periods of several months at a time and thus have ample opportunity to become accustomed to one another. Our study also reveals that the tendency of female guppies to school with familiar fish declines as the group size in which they naturally live increases. Preferences are strong when there are small numbers of females in a pool, but diminish thereafter. This indicates that the expression of familiarity is constrained by group size. The basis of recognition and the consequences of schooling preferences for familiar individuals are discussed.     

Attractiveness of the male Acheta domesticus calling song to females

1. Most crickets first demonstrated positive phonotaxis to 65 dB CSs having a 53-62 ms SP by day 3 following the imaginal molt (Fig. 3B). The onset of copulatory readiness occurred on average at 3.2 days. 2. The attractive range of SPs for most females became progressively broader as they aged (Fig. 4). Three to 4-day-old females were attracted to a smaller number of CS SPs than were 20-21 day old females (Fig. 4). 3. Older, less selective females did not typically respond to the same range of CS SPs (Fig. 6). However, they were more likely to respond to some SPs (especially 50 ms) than to others (Fig. 7). 4. The phonotactic threshold decreased from 95 dB or greater on day 0 to a mean of 55 dB by day 3, during a period of increasing JHIII biosynthesis, and thereafter remained at that level (Fig. 8). 5. During a period of maximal JHIII production, 3-5 day-old females usually responded to 4 of the 7 SPs presented (Fig. 8). Females older than 12 days were unselective for CS SP, and JHIII synthesis remained at a level below the peak production on day 4 (Fig. 8). 6. Older females, that were unselective for CS SP, became as selective as 3 to 5-day-old females within 4 days of topical application of JHIII (Figs. 9-11).     

天然杀伤(NK)细胞与靶细胞相互作用的研究

本文对NK细胞与正常的,以及经低温、加热、超声、辐射、单糖、蛋白酶、和/或环己亚胺处理的靶细胞(AV、1C2、YAC-1、R.1.1,R.1.X)的相互作用进行了研究。并且与混合淋巴细胞培养产生的细胞毒作用进行了比较。试验并对来自L 5178 Y的一对变株AV(NK不敏感株)和1C2(NK敏感株)作了FACS分析。结果表明:NK细胞对多种瘤细胞均有杀伤作用,不受H-2限制,NK细胞介导的这一细胞毒作用可能需要一个完整的,有代谢活性的靶细胞结构。蛋白酶和环己亚胺处理能显著降低NK细胞的活性。FACS分析结果表明:1C2能特异地与抗Gg 3cer糖脂的单抗结合,而AV则不能。以上提示:NK细胞有它一定的识别作用。糖蛋白和/或糖脂可能是NK细胞所识别的靶的结构。     

Structural analysis of EcoRI-DNA complexes as revealed by electron microscopy

Electron microscopy of negatively stained isolated restriction enzyme EcoRI revealed particle projections with triangular or square outlines, indicating that the enzyme, in its tetrameric state, is tetrahedron-like. The two dimers making up the tetramer appear to be arranged in two planes orthogonal to each other. Complexes formed by EcoRI with the plasmids pBR322 or pGW10 were investigated by electron microscopic spreading techniques. In the presence of Mg²⁺, EcoRI was bound to the DNA molecules to form pearl necklace-like aggregates. The number of bound EcoRI particles was much higher as the sum of EcoRI-and 5..AATT..3 sites (with exceptions, the 5..AATT..3 sites may function as one type of EcoRI^* sites) along the DNAs, indicating unspecific binding. In the absence of Mg²⁺, EcoRI was bound to the DNA only at the recognition site for EcoRI and the sites where the tetranucleotide sequence 5..AATT..3 was present. A direct correlation of the local concentrations of the bases A and T within the flanking sequences of the binding sites with the frequency of EcoRI to the DNA was observed. Dimers and tetramers of the enzyme was found to bind to the DNA. Tetramers occasionally exhibited two binding sites for DNA as indicated by the observation of DNA loops originating at the sites of bound tetrameric EcoRI particles.Abbreviations BAC Benzyldimethylalkylammoniumchloride - bp base pairs - Kb kilobases - SDS sodium dodecylsulfate Enzymes (EC 3.1.23.13) Restrictionendonuclease EcoRI - (EC 3.1.23.21) Restrictionendonuclease HindIII - (EC 3.1.23.37) Restrictionendonuclease SalGI Dedicated Professor H. G. Schlegel on occasion of this 60th birthday     

Molecular Simulation and the Aggregation of the Heavy Fractions in Crude Oils

The use of Molecular Simulation in the study of aggregates of the molecules of the heavy fractions of crude oils is reviewed. Molecular Mechanics calculations of aggregates of asphaltenes having a single large aromatic region (continental type) and others having smaller aromatic regions connected by alkyl chains (archipelago type) are discussed in terms of the molecular recognition processes present in petroleum. Stacking of the aromatic regions was the most important process in the formation of aggregates of asphaltenes of the continental type with some unfavorable contributions from its saturated rings and alkyl side chains. The steric interference of these groups limits the growth of the aggregates to a small number of molecules. The asphaltenes of the archipelago type showed more complex aggregates because some molecules act as bridges and tangling between them may occur. The interaction of the asphaltene aggregates with resin molecules was analyzed and it was found that the high selectivity for some sites of the asphaltenes explains the specificity of the resins for its own crude oil.     

Zinc-binding Domain of the Bacteriophage T7 DNA Primase Modulates Binding to the DNA Template

The zinc-binding domain (ZBD) of prokaryotic DNA primases has been postulated to be crucial for recognition of specific sequences in the single-stranded DNA template. To determine the molecular basis for this role in recognition, we carried out homolog-scanning mutagenesis of the zinc-binding domain of DNA primase of bacteriophage T7 using a bacterial homolog from Geobacillus stearothermophilus. The ability of T7 DNA primase to catalyze template-directed oligoribonucleotide synthesis is eliminated by substitution of any five-amino acid residue-long segment within the ZBD. The most significant defect occurs upon substitution of a region (Pro-16 to Cys-20) spanning two cysteines that coordinate the zinc ion. The role of this region in primase function was further investigated by generating a protein library composed of multiple amino acid substitutions for Pro-16, Asp-18, and Asn-19 followed by genetic screening for functional proteins. Examination of proteins selected from the screening reveals no change in sequence-specific recognition. However, the more positively charged residues in the region facilitate DNA binding, leading to more efficient oligoribonucleotide synthesis on short templates. The results suggest that the zinc-binding mode alone is not responsible for sequence recognition, but rather its interaction with the RNA polymerase domain is critical for DNA binding and for sequence recognition. Consequently, any alteration in the ZBD that disturbs its conformation leads to loss of DNA-dependent oligoribonucleotide synthesis.     

Sequence-dependent structural variation in DNA undergoing intrahelical inspection by the DNA glycosylase MutM

MutM, a bacterial DNA-glycosylase, plays a critical role in maintaining genome integrity by catalyzing glycosidic bond cleavage of 8-oxoguanine (oxoG) lesions to initiate base excision DNA repair. The task faced by MutM of locating rare oxoG residues embedded in an overwhelming excess of undamaged bases is especially challenging given the close structural similarity between oxoG and its normal progenitor, guanine (G). MutM actively interrogates the DNA to detect the presence of an intrahelical, fully base-paired oxoG, whereupon the enzyme promotes extrusion of the target nucleobase from the DNA duplex and insertion into the extrahelical active site. Recent structural studies have begun to provide the first glimpse into the protein-DNA interactions that enable MutM to distinguish an intrahelical oxoG from G; however, these initial studies left open the important question of how MutM can recognize oxoG residues embedded in 16 different neighboring sequence contexts (considering only the 5'- and 3'-neighboring base pairs). In this study we set out to understand the manner and extent to which intrahelical lesion recognition varies as a function of the 5'-neighbor. Here we report a comprehensive, systematic structural analysis of the effect of the 5'-neighboring base pair on recognition of an intrahelical oxoG lesion. These structures reveal that MutM imposes the same extrusion-prone ("extrudogenic") backbone conformation on the oxoG lesion irrespective of its 5'-neighbor while leaving the rest of the DNA relatively free to adjust to the particular demands of individual sequences.     

Translation elongation regulates substrate selection by the signal recognition particle

The signal recognition particle (SRP) is a universally conserved cellular machinery responsible for delivering membrane and secretory proteins to the proper cellular destination. The precise mechanism by which fidelity is achieved by the SRP pathway within the in vivo environment is yet to be understood. Previous studies have focused on the SRP pathway in isolation. Here we describe another important factor that modulates substrate selection by the SRP pathway: the ongoing synthesis of the nascent polypeptide chain by the ribosome. A slower translation elongation rate rescues the targeting defect of substrate proteins bearing mutant, suboptimal signal sequences both in vitro and in vivo. Consistent with a kinetic origin of this effect, similar rescue of protein targeting was also observed with mutant SRP receptors or SRP RNAs that specifically compromise the kinetics of SRP-receptor interaction during protein targeting. These data are consistent with a model in which ongoing protein translation is in constant kinetic competition with the targeting of the nascent proteins by the SRP and provides an important factor to regulate the fidelity of substrate selection by the SRP.