Organic matter chemistry and dynamics in clear-cut and unmanaged hardwood forest ecosystems

Forest harvesting alters the organic matter cycle by changing litter inputs and the decomposition regime. We hypothesized that these changes would result in differences in organic matter chemistry between clear-cut and uncut watershed ecosystems. We studied the chemistry of soil organic matter (SOM), and dissolved organic carbon (DOC) in soil solutions and stream samples in clear-cut and uncut sites at the Hubbard Brook Experimental Forest in New Hampshire using DOC fractionation techniques and solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy.Alkyl-C (aliphatic compounds) and O-alkyl-C (carbohydrates) were the largest C fractions in soil and dissolved organic matter at Hubbard Brook. Alkyl-C ranged from 29–48% of soil C, 25–42% of soil solution C, and 22–42% of streamwater DOC. Carbohydrates comprised 32–49%, 36–43%, and 29–60% of C in soils, solutions, and streamwater, respectively. In both soils and soil solutions, the carbohydrate fraction decreased with increasing soil depth, while the aromaticity of organic matter increased with depth. There were no significant differences in the structural chemistry of SOM between clear-cut and uncut watersheds.The aromatic-C fractions in soil solutions at the clear-cut site ranged from 12–16%, approximately 40% greater than at the uncut site (8.5–11%). Thus, clear-cutting has resulted in the leaching of more highly decomposed organic matter, and depletion of more aliphatic compounds in the soluble organic pool. Because DOC fluxes are small compared to the SOM pool, large differences in soil solution chemistry do not substantially alter the overall composition of SOM. While the organic chemistry of stream DOC varied greatly among 3 sampling dates, there were no obvious clear-cutting effects. Thus, temporal variations in flowpaths and/or in-stream processes appear to be more important than disturbance in regulating the organic carbon chemistry of these streams.     

Human heat shock gene expression and the modulation of plasma membrane Na+, K+-ATPase activity

Benzodiazepine receptor solubilized from bovine cortical membranes was bound to a new benzodiazepine affinity column, the synthesis of which is described. Bio-specific elution with the benzodiazepine compound chlorazepate resulted in the elution of fractions highly enriched in specific binding for the GABA receptor agonist muscimol. Specific activity for [³H]muscimol binding was >1.3 nmol/mg protein. It is shown that [³H]flunitrazepam binding activity can be recovered by removal of chlorazepate from the purified fraction. These results strongly support a model which suggests that the 2 binding sites reside on the same physical entity.     

Flavonoid synthesis in Petunia hybrida: partial characterization of dihydroflavonol-4-reductase genes

In this paper we describe the organization and expression of the genes encoding the flavonoid-biosynthetic enzyme dihydroflavonol-4-reductase (DFR) in Petunia hybrida. A nearly full-size DFR cDNA clone (1.5kb), isolated from a corolla-specific cDNA library was compared at the nucleotide level with the pallida gene from Antirrhinum majus and at the amino acid level with enzymes encoded by the pallida gene and the A1 gene from Zea mays.The P. hybrida and A. majus DFR genes transcribed in flowers contain 5 introns, at identical positions; the three introns of the A1 gene from Z. mays coincide with first three introns of the other two species. P. hybrida line V30 harbours three DFR genes (A, B, C) which were mapped by RFLP analysis on three different chromosomes (IV, II and VI respectively).Steady-state levels of DFR mRNA in the line V30 follow the same pattern during development as chalcone synthase (CHS) and chalcone flavanone isomerase (CHI) mRNA. Six mutants that accumulate dihydroflavonols in mature flowers were subjected to Northern blot analysis for the presence of DFR mRNA. Five of these mutants lack detectable levels of DFR mRNA. Four of these five also show drastically reduced levels of activity for the enzyme UDPG: flavonoid-3-O-glucosyltransferase (UFGT), which carries out the next step in flavonoid biosynthesis; these mutants might be considered as containing lesions in regulatory genes, controlling the expression of the structural genes in this part of the flavonoid biosynthetic pathway. Only the an6 mutant shows no detectable DFR mRNA but a wild-type level for UFGT activity. Since both an6 and DFR-A are located on chromosome IV and DFR-A is transcribed in floral tissues, it is postulated that the An6 locus contains the DFR structural gene. The an9 mutant shows a wild-type level of DFR mRNA and a wild-type UFGT activity.     

Modeling the precision and robustness of Hunchback border during Drosophila embryonic development

During anterior-posterior axis specification in the Drosophila embryo, the Hunchback (Hb) protein forms a sharp boundary at the mid-point of the embryo with great positional precision. While Bicoid (Bcd) is a known upstream regulator for hb expression, there is evidence to suggest that Hb effectively filters out “noisy” data received from varied Bcd gradients. We use mathematical models to explore simple regulatory networks which filter out such noise to produce a precise Hb boundary. We find that in addition to Bcd and Hb, at least one freely evolving protein is necessary. An automated search yields a number of examples of three-protein networks exhibiting the desired precision. In all such networks, Hb diffuses much slower than the third protein. In addition, the action of Hb on the third protein is the opposite of the action of the third protein on hb (i.e. if Hb activates the third protein, then the third protein inhibits hb expression, and vice versa). Most of the discovered systems satisfy the known biological properties, that Bcd activates hb, and that Hb activates its own expression. We find that all network topologies satisfying these constraints arise among the networks exhibiting the desired precision. Investigating the dynamics of these networks, we find that under a general class of non-uniform initial conditions, Bcd can be eliminated from the system and the spatiotemporal evolution of these two proteins alone is sufficient to recapture the dynamics. We hypothesize that Bcd is needed only to spatially disturb the gradient of the third protein, and then becomes unnecessary in the further evolution of the Hb border. This provides a possible explanation as to why the Hb dynamics are robust under perturbations of the Bcd gradient. Under this hypothesis, other proteins would be able to assume the role of Bcd in our simulations (possibly in the case of evolutionary divergences or a redundancy in the process), with the only constraint that they act to positively regulate hb.     

Remodeling of the human papillomavirus type 11 replication origin into discrete nucleoprotein particles and looped structures by the E2 protein

The human papillomavirus (HPV) DNA replication origin (ori) shares a common theme with many DNA control elements in having multiple binding sites for one or more proteins spaced over several hundreds of base pairs. The HPV type 11 ori spans 103 bp and contains three palindromic E2 binding sites (E2BS-2, E2BS-3, and E2BS-4) for the dimeric E2 ori binding protein. These sites are separated by 64 and 3 bp. E2BS-1 is located 288 bp upstream of E2BS-2 and is not required for efficient transient or cell-free replication. In this study, electron microscopy was used to visualize complexes of HPV-11 DNA ori bound by purified E2 protein. DNA containing only E2BS-2 showed a single E2 dimer bound. DNA containing E2BS-3 and E2BS-4 showed two side-by-side E2 dimers, while DNA containing E2BS-2, E2BS-3, and E2BS-4 exhibited a large disk/ring-shaped protein particle bound, indicating that the DNA had been remodeled into a discrete complex, likely containing an E2 hexamer. With all four binding sites present, up to 27% of the DNA molecules were arranged into loops by E2, the majority of which spanned E2BS-1 and one of the other three sites. Studies on the dependence of looping on salt, ATP, and DTT using full-length E2 and an E2 protein containing only the carboxyl-terminal DNA binding and protein dimerization domain suggest that looping is dependent on the N-terminal domain and factors that may affect the manner in which E2 scans DNA for binding sites. The role of these structures in the modeling and regulation of the HPV-11 ori is discussed.     

CD4+CD25+调节性T细胞的外周维持

CD4 CD25 调节性T细胞作为一种抑制性T细胞功能亚群,在维持机体的免疫自稳和免疫耐受方面发挥了关键作用。该作用的发挥与其外周细胞库的维持密切相关。新近的研究显示CD4 CD25 调节性T细胞主要通过两种机制来维持其外周细胞库,一些功能分子参与其中。