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951.
Primosomal protein cascades load the replicative helicase onto DNA. In Bacillus subtilis a putative primosomal cascade involving the DnaD-DnaB-DnaI proteins has been suggested to participate in both the DnaA and PriA-dependent loading of the replicative helicase DnaC onto the DNA. Recently we discovered that DnaD has a global remodelling DNA activity suggesting a more widespread role in bacterial nucleoid architecture. Here, we show that DnaB forms a "square-like" tetramer with a hole in the centre and suggest a model for its interaction with DNA. It has a global DNA remodelling activity that is different from that of DnaD. Whereas DnaD opens up supercoiled DNA, DnaB acts as a lateral compaction protein. The two competing activities can act together on a supercoiled plasmid forming two topologically distinct poles; one compacted with DnaB and the other open with DnaD. We propose that the primary roles of DnaB and DnaD are in bacterial nucleoid architecture control and modulation, and their effects on the initiation of DNA replication are a secondary role resulting from architectural perturbations of chromosomal DNA.  相似文献   
952.
953.
We derive an analytic expression for site-specific stationary distributions of amino acids from the structurally constrained neutral (SCN) model of protein evolution with conservation of folding stability. The stationary distributions that we obtain have a Boltzmann-like shape, and their effective temperature parameter, measuring the limit of divergent evolutionary changes at a given site, can be predicted from a site-specific topological property, the principal eigenvector of the contact matrix of the native conformation of the protein. These analytic results, obtained without free parameters, are compared with simulations of the SCN model and with the site-specific amino acid distributions obtained from the Protein Data Bank. These results also provide new insights into how the topology of a protein fold influences its designability, i.e., the number of sequences compatible with that fold. The dependence of the effective temperature on the principal eigenvector decreases for longer proteins, as a possible consequence of the fact that selection for thermodynamic stability becomes weaker in this case.  相似文献   
954.
An internally truncated C gene of adr hepatitis B virus core antigen with long internal deletion (aa81–aa116) (ΔHBcAg with 36aa truncation) was expressed in Saccharomyces cerevisiae and the products (ΔrHBcAg) were purified from a crude lysate of the yeast by three steps: Sephrose CL-4B chromatography, sucrose step-gradient ultracentrifugation and CsCl-isopycnic ultracentrifugation. Results of ELISA test and density analysis of CsCl-isopycnic ultracentrifugation indicated that the purified products (ΔrHBcAg protein) with HBeAg antigenicity mainly located at the densities of 1.23 g ml−1. Observation and analysis of the purified ΔrHBcAg products by AFM indicated that the ΔrHBcAg (core) protein produced in S. cerevisiae could self-assemble into three or more size classes of core particles which exhibited a polymorphous distribution of ΔrHBcAg (core) particles. These different size classes of core particles mainly centred on the range whose mean diameter was from 10 nm to 48 nm, especially on the position of 11 nm, 15.6 nm and the range from 27 nm to 41 nm, respectively. Furthermore, the most number of core particles mainly centred on the range whose mean diameter was from 27 nm to 41 nm. These results above indicated that the truncated internal long fragment (aa81–aa116) probably had no effect on self-assembly of the HBcAg core particles which implied the internal length fragment (aa81–aa116) was not the sole domain for self-assembly of HBcAg dimer or the truncated HBcAg protein subunit formed the fresh interactive domain with each other. These initial results above by AFM analysis were very important for further research on the self-assembly, ultrastructure, subunit interaction and core internal deletion mutant (CIDM) function of HBcAg core particles.  相似文献   
955.
Conditions favoring differentiation and stabilization of the life cycle of the yeast Pachysolen tannophilus have been studied. When concentrations of the carbon source in the medium were lower than 100 g/l, it was found to be favorable to the mating of vegetative cells, both haploid and diploid. The addition of nitrogen and sulfur sources to the medium influenced the life phases of haploid cells and partially stabilized the vegetative growth of diploid cells. Enrichment of the nutrient medium with potassium, vitamins, and microelements was shown to be necessary for the formation and maturation of conjugated ascospores. Microelements, vitamins, and phosphorus in excessive amounts activated conjugation but did not provide for the distinct phases of formation of unconjugated asci and spores in the diploid cells. Possible reasons for the unstable diplophase in the yeast P. tannophilus have been discussed.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 483–488.Original Russian Text Copyright © 2005 by Bolotnikova, Mikhailova, Shabalina, Bodunova, Ginak.  相似文献   
956.
Proton motive force (pmf) is physiologically stored as either a ΔpH or a membrane potential (Δψ) across bacterial and mitochondrial energetic membranes. In the case of chloroplasts, previous work (Cruz et al. 2001, Biochemistry 40: 1226–1237) indicates that Δψ is a significant fraction of pmf, in vivo, and in vitro as long as the activities of counterions are relatively low. Kinetic analysis of light-induced changes in the electrochromic shift (ECS) in intact leaves was consistent with these observations. In this work, we took advantage of the spectroscopic properties of the green alga, Chlamydomonas reinhardtii, to demonstrate that light-driven Δψ was stored in vivo over the hours time scale. Analysis of the light-induced ECS kinetics suggested that the steady-state Δψ in 400 μmol photons m−2 s−1 red light was between 20 and 90 mV and that this represented about 60% of the light-induced increase in pmf. By extrapolation, it was surmised that about half of total (basal and light-induced) pmf is held as Δψ. It is hypothesized that Δψ is stabilized either by maintaining low chloroplast ionic strength or by active membrane ion transporters. In addition to the strong implications for regulation of photosynthesis by the xanthophyll cycle, these results imply that pmf partitioning is important across a wide range of species.  相似文献   
957.
We report a case of turnover between an alpha (GN) and a beta male (R7) and its effects in a troop of provisioned Japanese macaques (Macaca fuscata fuscata) in Shiga-Heights, Nagano Prefecture, Japan. The aggression between the 2 males was caused by the intrusion of GN towards the consort of R7. R7 received support from his brother and mother, and consequently defeated GN. After the turnover, R7 attacked GN frequently, which may have functioned to stabilize the dominance relationship between them. Also, R7 selectively attacked females friendly to GN soon after the turnover. Although we never observed polyadic aggression among males during the stable dominance period, 20 cases of polyadic aggression occurred among the 6 highest-ranked males in the 2 days following the turnover, and one case occurred on the fourth day. R7 and GN formed stable conservative alliances for attacking subordinate males. Males that did not participate in the turnover began to form revolutionary coalitions to attack higher-ranking males, but they were thwarted by the conservative coalitions between the dominants. Mutualism was a plausible explanation for the patterns of coalition formation because most of them were conservative with little associated cost. Seven females had a high proximity index (C-score) to GN before the turnover, but a significantly lower proximity index after the turnover. On the day of the turnover, 6 non-lactating females suddenly became receptive, suggesting that the turnover induced immediate receptivity in the females.  相似文献   
958.
Nearest neighbor analysis of immunocytolocalization experiments indicates that the enzymes glyceraldehyde-3-P dehydrogenase, triose-P isomerase and aldolase are located close to one another in the pea leaf chloroplast stroma, and that aldolase is located close to sedoheptulose bisphosphatase. Direct transfer of the triose phosphates between glyceraldehyde-3-P dehydrogenase and triose-P isomerase, and from glyceraldehyde-3-P dehydrogenase and triose-P isomerase to aldolase, is then a possibility, as is direct transfer of sedoheptulose bisphosphate from aldolase to sedoheptulose bisphosphatase. Spatial organization of these enzymes may be important for efficient CO2 fixation in photosynthetic organisms. In contrast, there is no indication that fructose bisphosphatase is co-localized with aldolase, and direct transfer of fructose bisphosphate from aldolase to fructose bisphosphatase seems unlikely.  相似文献   
959.
Highly ordered lipids adsorbed or grafted on surfaces are known to provide protection and lubrication custom engineered surfaces. We have used atomic force microscopy (AFM) to measure adhesion and frictional properties of the outermost surfaces of a variety of human hairs with the aim of both understanding the role of 18-methyleicosanoic acid (18-MEA), an unusual branched-chain fatty acid covalently bound to the cuticle surface, and investigating how treatments or the ethnic origin affect this layer. Results show that an unmodified silicon nitride AFM tip is able to detect changes at the hair surface that can be related to the absence or presence of this layer due to treatment conditions and in particular that this monolayer has a lubricant effect.  相似文献   
960.
Polychlorinated biphenyls (PCBs) are a family of 209 isomers (congeners) with a wide range of toxic effects. In structural terms, they are of two types: those with and those without chlorines at the ortho positions (2, 2', 6 and 6'). Only 20 congeners have no ortho chlorines. Three of these are bound by the aryl hydrocarbon receptor and are one to four orders of magnitude more toxic than all others. A monoclonal antibody, S2B1, and its recombinant Fab have high selectivity and nanomolar binding affinities for two of the most toxic non-ortho-chlorinated PCBs, 3,4,3',4'-tetrachlorobiphenyl and 3,4,3',4',5'-pentachlorobiphenyl. To investigate the basis for these properties, we built a three-dimensional structure model of the S2B1 variable fragment (Fv) based on the high-resolution crystallographic structures of antibodies 48G7 and N1G9. Two plausible conformations for the complementarity-determining region (CDR) H3 loop led to two putative PCB-binding pockets with very different shapes (models A and B). Docking studies using molecular mechanics and potentials of mean force (PMF) indicated that model B was most consistent with the selectivity observed for S2B1 in competition ELISAs. The binding site in model B had a deep, narrow pocket between V(L) and V(H), with a slight constriction at the top that opened into a wider pocket between CDRs H1 and H3 on the antibody surface. This binding site resembles those of esterolytic antibodies that bind haptens with phenyl rings. One phenyl ring of the PCB fits into the deep pocket, and the other ring is bound in the shallower one. The bound PCB is surrounded by the side chains of TyrL91, TyrL96 and TrpH98, and it has a pi-cation interaction with ArgL46. The tight fit of the binding pocket around the ortho positions of the bound PCBs indicates that steric hindrance of ortho chlorines in the binding site, rather than induced conformational change of the PCBs, is responsible for the selectivity of S2B1.  相似文献   
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