Mutational effect of the “- 35” element of sorghumpsbA gene promoter

Mutations of the first position T and the third position G in TTGACA, the " - 35" element of sorghum psbA gene promoter, were induced using chemically synthesized 20 nt oligonucleotide primer. Three mutants were produced: ATTACA, GTGACA, and ATGACA. Then the protein binding affinity of the mutants and the wild type sorghum psbA gene promoter was tested in a spinach chloroplast protein extract system. Gel retardation assay of the wild type showed a strong protein-binding band. On the other hand, the protein-binding band of the mutant resulting from single base mutation, ATGACA or GTGACA, showed reduced intensity, while that of the mutant resulting from double base mutation, ATTACA, showed increased intensity. It is thus shown that the " - 35" element plays an important role in controlling the binding between psbA gene promoter and the specific chloroplast proteins; mutation of a single base may exert a substantial influence on the binding affinity.     

MD5加密算法在Web程序中的应用

MD5报程序中的相关应用,并在研究了现存算法对数据加密的缺点的基础上,提出了一种用MD5算法加密口令的改进方案.     

金属载体上原位合成ZSM-5分子筛

以正硅酸乙酯(TEOS)和NaAlO2作为硅源和铝源，四乙基氢氧化铵(TEAOH)作为模板剂，用水热合成法在经表面处理的金属载体上原位合成了ZSM-5分子筛涂层，并采用BET、XRD、SEM等表征技术，研究了金属材料的处理方法、合成时间及次数等因素对ZSM-5分子筛涂层的结晶度、比表面积、覆盖率和涂层热牢固度的影响。结果表明，用原位合成法可以在金属载体上制得结晶度高、热牢固度好的ZSM-5涂层。     

PdCu／ZSM－5催化剂上乙醇一步合成乙酸乙酯反应机理的研究

本文采用程序升温脱附（ＴＰＤ）法、程序升温表面反应（ＴＰＳＲ）法和微反－色谱技术。综合考察了在ＰｄＣｕ／ＺＳＭ－５催化剂上，乙醇、乙醛、乙酸、氧等的吸附、脱附性能，以及不同条件下反应产物的分布规律，推测出乙醇在该催化剂上气相催化一步合成乙酸乙酯过程中的复杂网络图及反应机理，为改善此催化剂性能和进行动力学研究提供了重要信息和依据．     

量子化学方法研究HZSM-5沸石结构酸性(Ⅳ)

HZSM-5沸石分子筛硅铝骨架结构基本单元为五元环,它通过氧桥联接而得到单元为四元环、六元环。本文采用CNDO/2半经验量子化学的方法,对HZSM-5沸石基本结构单元—四、五、六元环的电荷分布进行计算。依据Mortier等人处理y型沸石分子筛酸性的基本思想,从而得到了HZSM-5沸石分子筛酸性结构参数α_0。Barthomeuf等认为沸石分子筛可作为一个多元酸的电解质溶液,因此其质子酸度应用活度来表示。a_(H~+)=[H~+]f_(H~+),而活度系数f_(H~+)为结构参数乘以一个常数,f_(H~+)=Kα_0,我们取K=32,[H~+]=nH~+αN_(A_1)/Z_(cat),从理论上求出HZSM-5沸石分子筛在不同硅铝比时的活度,其结果和实验值相一致。这为从理论上计算HZSM-5沸石分子筛的酸性提供了一个参考方法。     

Isolation of human epidermal stem cells by adherence and the reconstruction of skin equivalents

The isolation of human epidermal stem cells is critical for their clinical applications. In the present study, we isolated three populations of epidermal keratinocytes according to their ability to adhere to collagen type IV: i.e., rapidly adhering (RA), slowly adhering (SA), and non-adhering (NA) cells. The aim of this study was to characterize RA cells and to investigate the possibility of using these cells for epidermis reconstruction. To identify RA cells, flow cytometric analysis was performed using anti-₆ integrin and anti-CD71 antibodies. RA cells express high levels of ₆ integrin and low levels of CD71, which are considered as markers of an epidermal stem cell nature. Furthermore, electron microscopy showed that RA cells are small and have a high nuclear to cytoplasmic ratio, whereas SA and NA cells have well-developed cellular organelles and abundant tonofilaments. Western blot analysis showed that RA cells are slow cycling and express p63, a putative epidermal stem cell marker, whereas SA and NA cells express c-Myc, which is known to regulate stem cell fate. To compare epidermal regenerative abilities, skin equivalents (SEs) were made using RA, SA, and NA cells. The epidermis constructed from RA cells was well formed compared to those formed from SA or NA cells. In addition, only SEs with RA cells expressed ₆ integrin and ₁ integrin at the basal layer. These results indicate that RA cells represent epidermal stem cells and are predominately comprised of stem cells. Therefore, the isolation of RA cells using a simple technique offers a potential route to their clinical application, because they are easily isolated and provide a high yield of epidermal stem cells.Received 2 July 2004; received after revision 20 August 2004; accepted 10 September 2004     

Acylphosphatase overexpression triggers SH-SY5Y differentiation towards neuronal phenotype

An acylphosphatase (AcPase) overexpression study was carried out on SH-SY5Y neuroblastoma cells, using a green fluorescent fusion protein (AcP-GFP), with GFP acting as a reporter protein. The cellular proliferation rate was significantly reduced by overexpression of AcPase by a factor of ten. In contrast, clones transfected with two inactive AcPase mutants showed a growth rate comparable to control cells. This suggests that AcPase catalyzes the proliferative down-regulation. AcPase-overexpressing clones showed a physiological mortality rate as assessed by an MTT reduction test and by evaluation of necrotic markers. DNA fragmentation analysis and assays of caspase-3 and poly (ADP-ribose) polymerase (PARP)-active fragments showed no evidence of any apoptotic pattern. AcPase overexpression led to a marked increase in PARP activity as well as Bcl-2 content; these are commonly up-regulated during differentiative processes in neuronal cells. In fact, the typical differentiation marker, growth-associated-protein 43, was significantly up-regulated. Microscopic observations also showed a clear increase in the differentiative phenotype in AcPase-overexpressing cells. Our results clearly show that AcPase plays a primary causative role in neuronal differentiation.Received 3 May 2004; accepted 25 May 2004     

Differential effects of monastrol in two human cell lines

The kinesin-related protein HsEg5 plays essential roles in mitotic spindle dynamics. Although inhibition of HsEg5 has been suggested as an aid in cancer treatment, the effects of such inhibition on human cells have not been characterized. Here we studied the effects of monastrol, an allosteric HsEg5 inhibitor, on AGS and HT29 cell lines and compared them to those of taxol. While both cell lines were similarly sensitive to taxol, AGS cells were more sensitive to monastrol. The differences in sensitivity were determined by the degree of inhibitory effect on cell proliferation, reversibility of monastrol-induced G2/M arrest, intracellular phenotypes and induction of apoptosis. In both cell lines, monastrol-induced apoptosis was accompanied by mitochondrial membrane depolarization and poly-ADP-ribose polymerase 1 cleavage. In AGS, but not HT29 cells, monastrol-induced apoptosis involved a prominent cleavage of procaspases 8 and 3. While in AGS cells, monastrol induced the formation of symmetric microtubule asters only, in HT29 cells, asymmetric asters were also formed, which may be related to specific HsEg5 functions in HT29 cells.Received 18 February 2004; received after revision 30 May 2004; accepted 16 June 2004