Self-splicing group I and group II introns encode homologous (putative) DNA endonucleases of a new family.

A new family of protein domains consisting of 50-80 amino acid residues is described. It is composed of nearly 40 members, including domains encoded by plastid and phage group I introns; mitochondrial, plastid, and bacterial group II introns; eubacterial genomes and plasmids; and phages. The name "EX1HH-HX3H" was coined for both domain and family. It is based on 2 most prominent amino acid sequence motifs, each encompassing a pair of highly conserved histidine residues in a specific arrangement: EX1HH and HX3H. The "His" motifs often alternate with amino- and carboxy-terminal motifs of a new type of Zn-finger-like structure CX2,4CX29-54[CH]X2,3[CH]. The EX1HH-HX3H domain in eubacterial E2-type bacteriocins and in phage RB3 (wild variant of phage T4) product of the nrdB group I intron was reported to be essential for DNA endonuclease activity of these proteins. In other proteins, the EX1HH-HX3H domain is hypothesized to possess DNase activity as well. Presumably, this activity promotes movement (rearrangement) of group I and group II introns encoding the EX1HH-HX3H domain and other gene targets. In the case of Escherichia coli restrictase McrA and possibly several related proteins, it appears to mediate the restriction of alien DNA molecules.     

四种鹭类繁殖生态生物学研究

本文对夜鹭,白鹭,黄鹭白鹭,池鹭混群在同一巢区的繁殖,种间协高及雏鸟生长进行进行了观察研究,其中黄嘴白路豫南大别山类新纪录,在此繁殖亦为首次发现。几种路在巢位,食性,取食活动和习性方面都表现出其混居同一巢地繁殖的种间协调性,符合高期假说。比较４种鹭鸟雏鸟生长过程中各生长参数。其中池鹭虽个体最小,但体重和各部位生长却对较快。     

影响大肠杆菌中外源基因表达的因素

大肠杆菌已经被广泛地应用于表达各种外源基因,但是,不同的外源基因在表达效率上却有很大的差异,文章综述了影响大肠杆菌中外源基因表达的因素,这将有助于认识大肠杆菌中外源基因表达的规律,以便采取有效的方法提高外源基因在大肠杆菌中的表达效率．     

Efficient extracellular production of hybrid E. coli heat-labile enterotoxin B subunits in a marine vibrio

Abstract Escherichia coli heat-labile enterotoxin B subunit (EtxB) has been proposed as a potential protein carrier for the delivery of heterologous peptides to target cells, particularly for the oral delivery of epitopes to the mucosal immune system. In this study, two extensions to the C-terminus of EtxB were genetically engineered that correspond to a well-characterized neutralising epitope of glycoprotein D from herpes simplex virus (EtxB-gD) and to the C-terminal nine amino acids from the 38 kDa subunit of HSV-encoded ribonucleotide reductase (EtxB-R2). Here we describe the extracellular secretion of the two hybrid EtxBs from a marine Vibrio harbouring a broad-host range inducible expression vector containing the hybrid genes. Large amounts of intact fusion proteins (15–20 mg per liter of culture) were secreted into the medium upon induction. These hybrid proteins maintained the receptor-binding activity of the native toxin as well as being cross-reactive with anti-EtxB and anti-heterologous peptide monoclonal antibodies.     

Inhibition of G1 phase cyclin dependent kinases by transforming growth factor β1

Transforming growth factor β1 (TGFβ1) inhibits epithelial cell proliferation late in the G1 phase of the cell cycle. We examined the effect of TGFβ1 on known late G1 cell cycle regulators in an attempt to determine the molecular mechanism of growth inhibition by this physiological inhibitor. The results demonstrate the TGFβ1 inhibits the late G1 and S phase specific histone H1 kinase activity of p33^cdk2. This inhibitiion is not dur to TGFβ1's effect on p33^cdk2 synthesis, but rather due to its negative effect on the late G1 phosphorylation of p33^cdk2. It is also shown that TGFβ1 inhibits both late G1 cyclin A and cyclin E associated histon H1 kinase activities. The inhibitor has no effects on the synthesis of cyclin E but to inhibit the synthesis of cyclin A protein in a cell cycle dependent manner. If TGFβ1 is added to cells which have progressed futher than 8 hours into G1, then it is without inhibitory effect on cyclin A synthesis. These effect on TGFβ1 on late G1 cell cycle regulators correlate well with its inhibitory effects on cellular growth and suggest that these G1 cyclin dependent kinases might serve as targets for TGFβ1-mediated growth arrest.     

Magnesium-deficiency potentiates free radical production associated with postischemic injury to rat hearts: Vitamin E affords protection

Preexisting magnesium deficiency may alter the susceptibility of rat hearts to postischemic oxidative injury (free radicals). This was examined in rats maintained for 3 weeks on a magnesium-deficient (Mg-D) diet with or without concurrent vitamin E treatment (1.2 mg/day, SC). Magnesium-sufficient (Mg-S) rats received the same diet supplemented with 100 mmol Mg/kg feed. Following sacrifice, isolated working hearts were subjected to 30-, 40-, or 60-min global ischemia and 30-min reperfusion. Postischemic production of free radicals was monitored using electron spin resonance (ESR) spectroscopy and spin trapping with -phenyl-N-tert butylnitrone (PBN, 3 mM final); preischemic and postischemic effluent samples were collected and then extracted with toluene. PBN/alkoxyl adduct(s) (PBN/RO·; _H = 1.93 G,_N = 13.63 G) were the dominant signals detected in untreated Mg-S and Mg-D postischemic hearts, with comparably higher signal intensities observed for the Mg-D group following any ischemic duration. Time courses of postischemic PBN/RO· detection were biphasic for both groups (maxima: 2–4 and 8.5–12.5 min), and linear relationships between the extent of PBN/RO· production and the severity of both mechanical dysfunction and tissue injury were determined. Following each duration of ischemia, Mg-D hearts displayed greater levels of total PBN adduct production (1.7 –2.0 times higher) and lower recovery of cardiac function (42–48% less) than Mg-S hearts. Pretreating Mg-D rats with vitamin E prior to imposing 40-min ischemia/reperfusion, led to a 49% reduction in total PBN/RO· production, a 55% lower LDH release and a 2.2-fold improvement in functional recovery, compared to untreated Mg-D hearts. These data suggest that magnesium deficiency predisposes postischemic hearts to enhanced oxidative injury and functional loss, and that antioxidants may offer significant protection against pro-oxidant influence(s) of magnesium deficiency.     

The molecular genetics of Alzheimer's disease

The major pathological characteristic of Alzheimer's disease (AD) is the abnormal deposition of β-amyloid peptide (Aβ) in the brain. In some early onset cases, the disease develops because of mutations in the gene coding for β-amyloid precursor protein (βAPP). However, the majority of AD families in the early onset subgroup are linked to a locus on chromosome 14. The genetic analysis and age of onset correlates of both the βAPP gene and the chromosome 14 locus are discussed. We speculate on the mechanisms by which the βAPP mutations cause the disease and discuss recent advances in βAPP processing that may be relevant to the pathogenesis of the late-onset (common) form of the disease. In addition, we review the association of theAPOE locus with late-onset familial and nonfamilial disease. Further work is required to establish the effects of this locus on disease occurrence, age of onset, and progression. The molecular pathology of ApoE in relation to AD development and the identification of the chromosome 14 gene will greatly contribute to a general pathogenic model of AD, and will clarify the role of βAPP and its derivatives.     

Guanine nucleotide regulatory protein alterations in young Milan hypertensive strain rats

Vascular smooth muscle cell membranes from prehypertensive rats of the Milan hypertensive strain (MHS) were used to examine adenylyl cyclase activity and its regulation by guanine nucleotide regulatory proteins (G-proteins). Basal adenylyl cyclase activity was similar in MHS and Milan normontensive strain (MNS) membranes. Forsokolin (10^?4 M) produced a significantly greater stimulatory response in MHS membranes, but this was not observed with NaF (10^?2 M). Isoporterenol (10^?4 M) caused a significantly decreased stimulation of adenylyl cyclase activity in MHS membranes, while prostaglandin E₁ (10^?5 M) produced similar responses in the two strains. G_i function and GTP responses, as observed by biphasic effects of GTP on isoproterenol-stimulated membranes, were similar in both strains. The levels of G_i2α and G_qα/G₁₁α were similar in the two strains, while the levels of G_sα (44 and 42 kDa forms) and the β-subunit were significantly reduced by ～20% in MHS membranes. The α-subunit of G_i3 was dramatically reduced by ～80% in MHS membranes. The affinities of β-adrenergic receptors for the antagonist, cyanophindolol, were similar in the two strains; however, the number of β-adrenoceptors was substantially reduced in MHS membranes. These findings may be of relevance to altered vascular reactivity and transmembrane ion distribution observed in the MHS.     

Determination of the backbone torsion angle ɛ in nucleic acids

Summary The multiplet structure of cross peaks in double-quantum-filtered COSY NMR spectra is analysed for those resonances that include passive heteronuclear couplings. Interestingly, the cross peak involving the sugar-ring protons H2ELINE" BORDER="0"> and H3ELINE" BORDER="0"> in nucleic acids display an E.COSY-type appearance exclusively when the backbone torsion angle ELINE" BORDER="0"> (C4ELINE" BORDER="0">-C3ELINE" BORDER="0">-O3ELINE" BORDER="0">-P) adopts a gauche(-) conformation. This observation allows an unambiguous analysis of the conformation around ELINE" BORDER="0">, without the knowledge of ³J_cp coupling constants.     

鲑鱼生长激素基因分泌型表达质粒的构建

生长激素(GH)是动物垂体前叶分泌的一种多肽类激素.应用分子重组及PCR等技术,构建了一种鲑鱼生长激素基因分泌型表达质粒pOsGH153,使编码鲑鱼生长激素成熟肽的序列克隆在大肠杆菌分泌型表达载体PIN-Ⅲ-ompA内,直接位于编码大肠杆菌外膜蛋白A信号肽序列的下游,在Lpp-Lac杂合启动子控制下,经IPTG诱导,分子量约23 000的鲑鱼生长激素在大肠杆菌中获得高效表达,该产物具有天然鲑鱼生长激素的免疫活性,直接分泌到细胞周质,而信号肽被自动剪除.