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991.
The COP9/signalosome (CSN) is known to remove the stimulatory NEDD8 modification from cullins. The activity of the fission yeast cullins Pcu1p and Pcu3p is dramatically stimulated when retrieved from csn mutants but inhibited by purified CSN. This inhibition is independent of cullin deneddylation but mediated by the CSN-associated deubiquitylating enzyme Ubp12p, which forms a complex with Pcu3p in a CSN-dependent manner. In ubp12 mutants, as in csn mutants, Pcu3p activity is stimulated. CSN is required for efficient targeting of Ubp12p to the nucleus, where both cullins reside. Finally, the CSN/Ubp12p pathway maintains the stability of the Pcu1p-associated substrate-specific adaptor protein Pop1p. We propose that CSN/Ubp12p-mediated deubiquitylation creates an environment for the safe de novo assembly of cullin complexes by counteracting the autocatalytic destruction of adaptor proteins. 相似文献
992.
Chitin is reported to stimulate mycorrhizas and antagonistic, lytic-enzyme producing soil microorganisms. Here mycorrhizal and non-mycorrhizal strawberry (Fragaria vesca) plants were grown in peat growth-substrate and in peat amended with chitin (Suppressor™). Chitinase and cellulase activity was determined and the plants were challenged by inoculation withPhytophthora fragariae, the causal agent of redcore disease. Disease resistance was only found in the mycorrhizal strawberry-chitin amendment treatment and depended on the duration of the mycorrhiza’s growth in the amended substrate before potting on to a chitin-free growth substrate. The practical application of chitin substrate amendment in the exploitation of mycorrhizal biological control is discussed. 相似文献
993.
Swain SL 《Microbes and infection / Institut Pasteur》2003,5(3):213-219
Memory T cells are derived directly from effector cells without need for additional antigen, TcR triggering or induced cytokines. A large fraction of effectors can become memory cells without division, supporting a default pathway with little further differentiation. This suggests that the same signals during infection/vaccination determine the extent and nature of both effector and memory cell development. 相似文献
994.
Effect of transcription on folding of the Tetrahymena ribozyme 总被引:1,自引:0,他引:1
995.
A field study was conducted in the Lower East Fork of the Little Miami River, a regulated stream in Clermont county, Ohio, to determine how changes in streamflow, water temperature and photo-period affect sediment microbial community structure. Surface sediment cores were collected from sampling stations spanning 60 river kilometers three to four times per year between October 1996 and October 1999. During the final year of the field study, water temperature, water depth, conductivity, total suspended solids, dissolved organic carbon, instantaneous streamflow velocity, sediment grain size and sediment organic matter were determined. Total microbial biomass was measured using the phospholipid phosphate technique (PLP) and ranged between 2 and 134 nmol PLP * g(-1) dry weight sediment with a mean of 25 nmol PLP * g(-1). Microbial community structure was determined using the phospholipid fatty acid analysis and indicated seasonal shifts in sedimentary microbial community composition. January to June sedimentary microbial biomass was predominately prokaryotic (60% +/- 2), whereas microeukaryotes dominated samples collected during the late summer (55% +/- 2.4) and fall (60% +/- 2). These changes were correlated with stream discharge and water temperature. Microbial community structure varied spatially about a reservoir with prokaryotic biomass dominant at upstream stations and eukaryotic biomass dominant at downstream stations. These findings reveal that sedimentary microbial communities in streams are dynamic responding to the seasonal variation of environmental factors. 相似文献
996.
THE SOP MODEL [INFORMATION PROCESSING IN ANIMALS: Memory Mechanisms, Erlbaum, Hillsdale, NJ, 1981, p. 5] is described in terms of its assumed stimulus representation, network characteristics, and rules for learning and performance. It is shown how several Pavlovian conditioning phenomena can be accounted on the basis of the model's presumed stimulus representation. Challenges to the SOP model prompted the adoption of a componential stimulus representation in: AESOP [Contemporary Learning Theories: Pavlovian Conditioning and the Status of Traditional Learning Theory, Erlbaum, Hillsdale, NJ, 1989, p. 149], this was a dual representation of the unconditioned stimulus (US), and C-SOP [Contemporary Learning: Theory and Application, Erlbaum, Mahwah, NJ, 2001, p. 23], this was a multi-component representation of the conditioned stimulus (CS). The assumption of a componential CS representation, where large numbers of elements can be separately learned about, necessitated a modification of the learning rule. The modified, "constrained" rule was found useful to explain timing characteristics of Pavlovian conditioned responses, as well as data offered by Rescorla [J. Exp. Psychol. Anim. Behav. Process. 26 (2000) 428; Q. J. Exp. Psychol. 54B (2001) 53; J. Exp. Psychol. Anim. Behav. Process. 28 (2002) 163] showing that stimuli trained in compound do not share the same quantitative fate. 相似文献
997.
This study compared dynamics of the germ cell population in two swine breeds that differ in prolifacy, White Composite (WC) and Meishan (MS), during fetal and neonatal life and in mature sows. Germ cell populations developed in a similar pattern in these two diverse breeds during fetal life. Maximal germ cell number was observed at 90 days postcoitum (dpc) in both WC and MS gilts, and substantial oogonial apoptosis was evident thereafter with approximately 30% of maximal numbers present at 25 days postpartum (dpp). Neither gilt nor sow germ cell number was correlated with maternal ovulation rate. Postnatal MS gilts had larger pools of primordial follicles and consistently greater proportions and numbers of primary and secondary follicles compared to postnatal WC gilts, indicative of enhanced follicular recruitment and primordial follicle activation. Occasional antral follicles were present in MS ovaries by 25 dpp and numerous surface follicles were observed at 56 dpp in MS but not WC ovaries, indicative of more rapid ovarian maturation and early onset of puberty. Total germ cell number is unlikely to influence or to predict subsequent ovulation rate. These observations highlight important developmental events during late fetal and early postnatal life that prepare the ovarian environment for early onset of puberty and subsequent ovulation in MS gilts. 相似文献
998.
The componential extension of SOP accounts for conditioned response (CR) timing in Pavlovian conditioning by assuming that learning accrues with relative independence to stimulus elements that are differentially occasioned during the duration of the conditioned stimulus (CS). SOP, using a competitive learning rule and the assumption that temporal learning emerges via resolution of what is equivalent to an "AX+BX-" discrimination, predicts a progressive increase in the latency of the CR over training, or what Pavlov refer to as "inhibition of delay." Other componential models, which use noncompetitive learning rules, do not predict inhibition of delay. Either type of model makes the prediction indicated, independently of the length of the CS-unconditioned stimulus (US) interval. We report two experiments that demonstrated inhibition of delay when rabbits were trained with relatively long, but not with short, CS-US intervals. To account for this divergence, we assumed that the SOP stimulus trace involves two kinds of elements, some with a temporally distributed pattern of activity over the duration of the CS duration, and some with a randomly distributed pattern. This stimulus representation, not only allows for inhibition of delay with long but not short CS-US intervals, but in combination with SOP's performance rule deduces CR's with "Weber variability." 相似文献
999.
Peptides possess appropriate pharmacokinetic properties to serve as cancer imaging or therapeutic targeting agents. Currently, only a small number of rationally-derived, labeled peptide analogues that target only a limited subset of antigens are available. Thus, finding new cancer targeting peptides is a central goal in the field of molecular targeting. Novel tumor-avid peptides can be efficiently identified via affinity selections using complex random peptide libraries containing millions of peptides that are displayed on bacteriophage. In vitro and in situ affinity selections may be used to identify peptides with high affinity for the target antigen in vitro. Unfortunately, it has been found that peptides selected in vitro or in situ may not effectively target tumors in vivo due to poor peptide stability and other problems. To improve in vivo targeting, methodological combinatorial chemistry innovations allow selections to be conducted in the environment of the whole animal. Thus, new targeting peptides with optimal in vivo properties can be selected in vivo in tumor-bearing animals. In vivo selections have been proven successful in identifying peptides that target the vasculature of specific organs. In addition, in vivo selections have identified peptides that bind specifically to the surface of or are internalized into tumor cells. In the future, direct selection of peptides for cancer imaging may be expedited using genetically engineered bacteriophage libraries that encode peptides with intrinsic radiometal-chelation or fluorescent sequences. 相似文献
1000.
Lining?TianEmail author Daniel?Brown Susan?Sibbald Marysia?Latoszek-Green 《Plant Molecular Biology Reporter》2003,21(2):175-175
β-Glucuronidase (GUS) and luciferase (LUC) reporter genes were introduced into white spruce (Picea glauca [Moench] Voss) cultured cells via particle bombardment. Transient expression of these genes was evaluated by extracting the
enzymes using 3 buffers. Different buffers resulted in significantly different sensitivities of GUS and LUC detection. In
the case of cobombardment, the buffer that gave high levels of expression of one reporter gene did not necessarily result
in a better detection of the second reporter gene. This study indicates that appropriate buffers should be used for maximum
detection of reporter genes. 相似文献