Evidence for the regulation of protein synthesis by a wheat germ phosphoprotein factor

A 48-kilodalton phosphoprotein, termed T-protein or pT, isolated from wheat germ and purified to homogeneity is found to inhibit the translation of tobacco mosaic virus (TMV) RNA in both wheat germ and reticulocyte lysates. The translation of TMV RNA in both systems was inhibited over 80% by 8 microM pT. There was no evidence to indicate that the reticulocyte lysate also contained a pT-like protein. pT was rapidly phosphorylated in the wheat germ and reticulocyte lysates. Although the relationship between pT phosphorylation and inhibition of protein synthesis is not known, there is evidence to indicate that complete phosphorylation of pT is not required for inhibition. Furthermore, no significant differences in the kinetics of inhibition of protein synthesis between prephosphorylated and unmodified pT were observed. Investigation of the mechanism of inhibition indicated that neither the aminoacylation of tRNA nor the elongation of nascent polypeptide chains was affected by pT. On the other hand, pT was found to prevent the formation of the 80S initiation complex. This action of pT was not due to the binding of pT to the ribosomes. However, the effect of pT was found to vary with the concentrations and types of mRNA used in the translational system. These results suggest that pT may interact with specific region(s) of the mRNA and prevent its translation. Alternatively, pT could block the translation of mRNA by binding to one or more of the initiation factors that interact with mRNA to facilitate mRNA binding to the 43S preinitiation complex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular cloning and nucleotide sequencing of oxyR, the positive regulatory gene of a regulon for an adaptive response to oxidative stress in Escherichia coli: homologies between OxyR protein and a family of bacterial activator proteins

Summary Treatment of Escherichia coli and Salmonella typhimurium cells with a low dose of hydrogen peroxide induces expression of a large number of genes, and confers resistance to oxidative stresses. The oxyR gene encodes a positive regulatory protein for a subset of these genes involved in the defense against oxidative damage. We cloned a DNA fragment that contains the E. coli oxyR region on a plasmid vector, and analyzed the nucleotide sequence of the gene. The amino acid sequence of OxyR protein, deduced from the nucleotide sequence, shows a high degree of homology to the sequences of a number of bacterial activator proteins including LysR, cysB, IlvY, MetR and NodD. The product of the oxyR gene identified by the maxicell procedure was a 34 kDa protein, which agrees with the size predicted from the nucleotide sequence of the gene.     

Structure of DNA hydration shells studied by Raman spectroscopy

We have used Raman scattering to study the water O-H stretching modes at approximately 3450 and approximately 3220 cm-1 in DNA films as a function of relative humidity (r.h.). The intensity of the 3220-cm-1 band vanishes as the r.h. is decreased from 98% to around 80%, which indicates that the hydrogen-bond network of water is disrupted in the primary hydration shell (which therefore cannot have an "ice-like" structure). The number of water molecules in the primary hydration shell was determined from the intensity of the approximately 3200-cm-1 band as about 30 water molecules per nucleotide pair. The approximately 3400-cm-1 O-H stretch band was used for determining the total water content, and this band persists at 0% r.h., implying that 5-6 tightly bound water molecules per nucleotide pair remain. The frequency of the approximately 3400-cm-1 O-H stretch mode is lower by 30 to 45 cm-1 in the primary hydration shell compared to free water. The water content as a function of r.h. obtained from these experiments agrees with gravimetric measurements. The disappearance of the approximately 3200-cm-1 band and the shift of the approximately 3400-cm-1 O-H stretch band provide a reliable way of measuring the hydration number of DNA.     

Oligosaccharide synthesis by enzymatic transglycosylation

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桂西壮族手皮纹的分析

本文对广西西部500例健康壮族大、中学生的手皮纹进行了观察分析,计算出各型指纹频率、指纹脊线总数、指纹频度指数、atd角度、a-b脊线数、τ距比、主线横向指数、皮纹花样出现率、掌褶纹出现率共九项基本参数,并将这些数值与汉族作了比较,桂西壮族的手纹与汉族既有相似之处,又有本民族的特点。     

Effects of Various Levels of CO(2) on the Induction of Crassulacean Acid Metabolism in Portulacaria afra (L.) Jacq

In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO₂ fixation (C₃) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C₃-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO₂ concentration and that these changes in CO₂ could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal (ca. 330 ppm), and high (950 ppm) CO₂ during the day with normal concentrations of CO₂ during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO₂ uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO₂ treatments. In well-watered plants, however, both low and high ambient concentrations of CO₂ tended to reduce organic acid concentrations, low concentrations of CO₂ reducing the organic acids more than high CO₂. It was concluded that exposing the plants to the CO₂ concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism.     

Laser-transected microtubules exhibit individuality of regrowth, however most free new ends of the microtubules are stable

To study the possible mechanism of microtubule turnover in interphase cells, we have used the 266-nm wavelength of a short-pulsed Nd/YAG laser to transect microtubules in situ in PtK2 cells at predefined regions. The regrowth and shrinkage of the transected microtubules have been examined by staining the treated cells with antitubulin mAb at various time points after laser irradiation. The results demonstrate that microtubules grow back into the transected zones individually; neither simultaneous growth nor shrinkage of all microtubules has been observed. The half-time of replacement of laser-dissociated microtubules is observed to be approximately 10 min. On the other hand, exposure of the core of the microtubule, which is expected to consist almost completely of GDP-tubulin, by transecting the internal regions of the microtubule does not render the remaining polymer catastrophically disassembled, and most transected microtubules with free minus ends do not quickly disappear. Taken together, these results suggest that most microtubules in cultured interphase cells exhibit some properties of dynamic instability (individual regrowth or shrinkage); however, other factors in addition to the hydrolysis of GTP-tubulin need to be involved in modulating the dynamics and the stability of these cytoplasmic microtubules.     

马铃薯未传粉子房离体培养诱导双单倍体植株

以MS为基本培养基,附加不同水平的生长素,培养未传粉马铃薯子房,经三年试验,从两个品种中获得了双单倍体的绿色小植株,(2n=2x=24);从分化绿苗力很强的球状愈伤组织中,又不断地分化出许多绿色小植株。绝大多数品种,都可以诱导出愈伤组织,一般诱导率为70％左右。品种的基因型和培养基中的生长素种类与水平在愈伤组织分化绿苗中起着重要作用。通过扦插和试管微型薯培养,可以大量繁殖试管苗,这为马铃薯单倍体育种提供了较有利的条件。