pH-dependent structural transition in rabbit skeletal troponin C

Although the crystal structure of troponin C is known (Herzberg, O., and James, M. N. G. (1985) Nature 313, 653-659; Sundaralingam, M., Bergstrom, R., Strasburg, G., Rao, S. T., Roychowdhury, P., Greaser, M., and Wang, B. C. (1985) Science 227, 945-948), its structure in solution, particularly under physiological conditions, has not been established. We examined the conformation of troponin C under a variety of conditions by measuring the distance between sites located in the N- and C-terminal domains using the technique of resonance energy transfer. The donor was the luminescent lanthanide ion Tb3+ bound at the low affinity metal sites in the N-terminal domain. The acceptor was 4-dimethylaminophenylazophenyl-4'-maleimide attached at Cys-98 in the C-terminal domain. The distance between these sites was found to be greater than 5.2 nm at pH 5.0, 2.7 nm at pH 6.8 for uncomplexed troponin C, and 4.1 nm for troponin C complexed with troponin I at pH 6.8. These findings suggest that uncomplexed troponin C undergoes a pH-dependent transition from an elongated conformation, compatible with the crystal structure at acidic pH, to a more compact conformation at neutral pH. When complexed with troponin I, troponin C adopts a conformation of intermediate length compared to the uncomplexed molecule at pH 6.8 and 5.0.     

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。     

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。