Construction and expression of nonsense suppressor tRNAs which function in plant cells

An Arabidopsis thaliana L. DNA containing the tRNA(TrpUGG) gene was isolated and altered to encode the amber suppressor tRNA(TrpUAG) or the ochre suppressor tRNA(TrpUAA). These DNAs were electroporated into carrot protoplasts and tRNA expression was demonstrated by the translational suppression of amber and ochre nonsense mutations in the chloramphenicol acetyltransferase (CAT) reporter gene. DNAs encoding tRNA(TrpUAG) and tRNA(TrpUAA) nonsense suppressor tRNAs caused suppression of their cognate nonsense codons in CAT mRNAs, with the tRNA(TrpUAG) gene exhibiting the greater suppression under optimal conditions for expression of CAT. The development of these translational suppressors which function in plant cells facilitates the study of plant tRNA gene expression and will make possible the manipulation of plant protein structure and function.     

毒黄素对黄嘌呤氧化酶作用的影响

利用从椰毒假单胞菌(Pseudomona cocovenenans)中所分离提取的毒黄素(toxoflavin)对黄嘌呤氧化酶(EC.1、2 3、2)作用的动力学试验表明,毒黄素是此酶的非必需激活剂,而且对以次黄嘌呤为底物的反应的激活作用明显高于以黄嘌呤为底物的反应。此激活作用属于部分混合型。这一结果为探寻毒黄素对人体的致毒机理提供了一条重要线索。     

外周损伤引起成年大鼠体感皮层的功能重组

为了了解外周神经损伤对体感皮层分域组构的影响,在成年大鼠上观察了切断坐骨神经(SC)前、即刻和切断后数周内后爪皮层代表区的改变。在盐酸氯胺酮麻醉下,用微电极记录后爪皮肤轻触刺激在对侧体感皮层工区诱发的多单位反应,得出后爪的皮层代表区图。在16例中,8例大鼠观察了切断SC的即时效应。结果表明,不但SC代表区丧失皮肤反应性,原隐神经(SA)代表区的皮肤反应性也明显下降或消失,同时神经元自发活动也明显减弱。另8例大鼠在切断后数周内做了1～3次重复测定。在最初几天,原SA代表区范围内多数记录点的皮肤反应性仍未恢复,但在原SC代表区内,一些记录点转而对SA皮肤轻触刺激起反应。在随后数周内SA代表区进行性地扩张,占领了大部分原SC代表区。这一结果说明成年大鼠外周神经损伤可导致体感皮层发生显著的重组改变。     

烙铁头蛇毒纤维蛋白原溶酶研究 Ⅰ分离纯化及理化性质(英文)

通过DEAE-SephadexA-50,DEAE-SepharoseCL-6B,MonoQ （FPLC）三步离子交换柱层析,纯化得到一新的纤维蛋白原溶酶,在碱性聚丙烯酰胺凝胶电泳和SDS-聚丙烯酰胺凝胶电泳上均呈单一的蛋白带。分子量为2600,等电点pl4.7;它是一个糖蛋白,含糖量6.4%,其中中性糖0.3%,已糖胺4.9%,唾液酸1.2%。烙铁头蛇毒纤维蛋白原溶酶TMVFg由187个氨基酸组成,含有较高的酸性氨基酸,此外甘氨酸含量也较高。TMVFg热稳定性强,而酸不稳定,在280 nm处具有典型的蛋白吸收峰,在无离子水中紫外消光系数E0.1%/280 nm=1.558。纯化的TMVFg具有较强的精氨酸酯酶活力,对苯甲酰-L-精氨酸乙酯（BAEE）的Km值为1.4×10[-3]M。TMVFg的活性受苯甲基丹磺酰氟（PMSF）抑制;乙二胺四乙酸（EDTA）对活性无影响。TMVFg不能使纤维蛋白原凝固,但能水解纤维蛋白原α、β链。纤溶实验表明TMVFg具有激活纤溶作用。纯化的烙铁头蛇毒纤维蛋白原溶酶对酪蛋白无作用,无出血活性,因而与凝血酶样酶、出血毒素及β-纤维蛋白原溶酶（OUYANG et al.,1977）明显不同。     

The effect of the length of direct repeats and the presence of palindromes on deletion between directly repeated DNA sequences in bacteriophage T7.

The frequency of genetic deletion between directly repeated DNA sequences in bacteriophage T7 was measured as a function of the length of the direct repeat. The non-essential ligase gene (gene 1.3) of bacteriophage T7 was interrupted with pieces of synthetic DNA bracketed by direct repeats of various lengths. Deletion of these 76 bp long inserts was too low to be measured when the direct repeats were less than 6 bp long. However, the frequency of deletion of inserts with longer direct repeats increased exponentially as the length of the repeats increased from 8 to 20 bp. When inverted repeats (palindromes) were designed in the midst of the insert there was essentially no increase in deletion frequency between 10 bp direct repeats. But, the same palindromic sequences increased the deletion frequency between 5 bp direct repeats by at least two orders of magnitude. Thus, in this system homology at the endpoints is a more important determinant of deletion frequency than is the presence of palindromes between the direct repeats.     

Evidence for a new Escherichia coli protein resembling a lysyl-tRNA synthetase.

The amino acid sequence deduced from the nucleotide sequence of an open reading frame adjacent to the frdA gene of Escherichia coli shows 30.5% identity with the C terminus of Escherichia coli lysyl-tRNA synthetases. The three motifs characteristic of aminoacyl-tRNA synthetases of class 2 are recognizable within this sequence.     

Role of sulphated tyrosine residue in influencing the biologic activity of human cholecystokinin-33

To evaluate the role of the sulphated tyrosine residue in position 27 in human cholecystokinin-33, parallel bioassay of the sulphated form of human cholecystokinin-33 and the unsulphated form of human cholecystokinin-33 was performed on the pancreatic protein secretion. Both peptides increased the protein output in a dose-related manner. However, the sulphated form possessed a considerably higher activity than the sulphated form. The relative potency of the unsulphated human cholecystokinin-33 compared to that of the sulphated human cholecystokinin-33 (taken as 1.0) was 0.08. From the results, it was suggested that the sulphated tyrosine may play an important role in controlling the activity of the longer molecular forms as well as that of the smaller forms of cholecystokinin.     

Isotope partitioning in the adenosine 3',5'-monophosphate dependent protein kinase reaction indicates a steady-state random kinetic mechanism

Isotope partitioning beginning with the binary E.MgATP and E.N-acetyl-Leu-Arg-Arg-Ala-Ser-Leu-Gly (Ser-peptide) complexes indicates that the kinetic mechanism for the adenosine 3',5'-monophosphate dependent protein kinase is steady-state random. A total of 100% of the initial radioactive E.MgATP complex is trapped as phospho-Ser-peptide at infinite Ser-peptide concentration at both low and high concentration of uncomplexed Mg2+, suggesting that the off-rate of MgATP from the E.MgATP.Ser-peptide complex is slow relative to the catalytic steps. Km for Ser-peptide in the trapping reaction decreases from 17 microM at low Mg2+ to 2 microM at high Mg2+, indicating that Mg2+ decreases the off-rate for MgATP from the E.MgATP complex. A total of 100% of the radioactive E.Ser-peptide complex is trapped as phospho-Ser-peptide at low Mg2+, but only 40% is trapped at high Mg2+ in the presence of an infinite concentration of MgATP, suggesting that the off-rate for Ser-peptide from the central complex is much less than catalysis at low but not at high Mg2+. In support of this finding, the Ki for Leu-Arg-Arg-Ala-Ala-Leu-Gly (Ala-peptide) increases from 0.27 mM at low Mg2+ to 2.4 mM at high Mg2+. No trapping was observed at either high or low Mg2+ for the E.MgADP complex up to a phospho-Ser-peptide concentration of 5 mM. Thus, it is likely that in the slow-reaction direction the kinetic mechanism is rapid equilibrium.(ABSTRACT TRUNCATED AT 250 WORDS)     

流行性感冒病毒重组株京生75-29 R2 T1及冷适应株31-广的基因分析

用聚丙烯酰胺凝胶电泳方法分析了流行性感冒病毒重组株京生75-29R2 T1(H3N2)及冷适应株31-广(H3N2)的RNA及多肽。重组株京生75-29R2 T1的HA及M基因系来自流行病毒亲本株/甲/北京/29/75(H3N2),而P_2、NA、NP及NS基因则来自温度敏感母株福R3(H2N2)。流行病毒株甲/穗/03/68(H3N2)在低温条件下经鸡胚尿囊腔传递24代而获得的冷适应疫苗毒株31-广(H3N2)其基因型与野毒株一致。     

The kinetics of the first wave of spermatogenesis in the newborn male mouse

A combination of autoradiography and air-dried techniques was used to calculate the duration of the major meiotic stages in the first wave of spermatogenesis in the newborn mouse. The data indicated that the entry into meiosis occurred asynchronously over 2 days, and the time required for each stage and the total cycle was constant. These time intervals were nearly identical with those estimated for adult animals in the present study and by other authors.