Purification and characterization of the deoxynucleoside monophosphate kinase of bacteriophage T5

Deoxynucleoside monophosphate kinase (dNMP kinase) of bacteriophage T5 (EC 2.7.4.13) was purified to apparent homogeneity from phage-infected Escherichia coli cells. Electrophoresis in sodium dodecyl sulfate-polyacrylamide gel showed that the enzyme has a molecular mass of about 29 kDa. The molecular mass of dNMP kinase estimated by analytical equilibrium ultracentrifugation turned out to be 29.14 +/- 3.03 kDa. These data suggest that the enzyme exists in solution as a monomer. The isoelectric point of dNMP kinase was found to be 4.2. The N-terminal amino acid sequence, comprising 21 amino acids, was determined to be VLVGLHGEAGSGKDGVAKLII. A comparison of this amino acid sequence and those of known enzymes with a similar function suggests the presence of a nucleotide-binding site in the sequenced region.     

Regulation of the conductance and resting potential by extracellular K+ in frog taste receptor cells

The effect of extracellular K+ on membrane currents was investigated by the patch clamp and fast perfusion techniques in frog (Rana temporaria) taste receptor cells (TRCs). When added to the bath, K+ increased the TRC conductance. The integral current and current fluctuations depended on the K+ concentration (2.5-90 mM) in the manner which suggested extracellular K+ to serve as a ligand activating ionic channels (potassium-activated (PA) channels). The influence of different ions on the PA current reversal potential indicated that the responsible channels are mainly permeable to K+ and H+. Relative permeabilities were estimated as P(H):P(K) = 3600:1. With 110 mM KCl in the patch pipette and 110 mM NaCl in the bath, isolated TRCs exhibited the resting potentials from -75 to -65 mV. When raised from 2.5 to 110 mM, extracellular K+ intensively depolarized TRCs. Membrane potential vs. K+ concentration displayed a slope of about 41 mV per logarithmic unit. This indicates that the K+ permeability of the TRC membrane dominates the other in setting the potential. With 10 mM K+ in the bath, the PA channels were the major contributor to setting the TRC resting potential. External K+ markedly increased the sensitivity of isolated TRCs to bath solution pH due to the activation of the PA channels suggesting their role in sour transduction.     

The effect of head-down hypokinesia on functional state of diaphragm in rats

The effects of long-term (21 days) head-down (-30 degrees) hypokinesia (HDH) on respiratory system and a functional state of diaphragm were investigated in rats. Minute ventilation, oesophageal and abdominal pressure, integrated electrical activity of diaphragm were measured in control and experimental group (after 21 days of HDH) of animals. The measurements were made in several body positions atresting and in occlusion breathing. The results indicate that HDH causes reduction in minute ventilation of lungs, decrease in orthostatic stability and functional reserve of the respiratory system capacity. It was established that the basic mechanism of HDH respiratory effects is contractile failure of diaphragm related to damage in excitation-contraction coupling in its muscular fibres.     

Acute lesions of the ventromedial hypothalamus reduce sympathetic activation and thermogenic changes induced by PGE1

The aim of this experiment was to evaluate the effects of an intracerebroventricular (icv) injection of prostaglandin E1 (PGE₁) on the sympathetic activation and the thermogenic changes in rats with acute lesions of the ventromedial hypothalamus (VMH). Four groups of six Sprague-Dawley male rats were anesthetized with ethyl-urethane. The firing rate of the sympathetic nerves innervating the interscapular brown adipose tissue (IBAT) and the colonic and IBAT temperatures were monitored both before and after one of the following treatments: 1) VMH lesion plus icv injection of PGE₁ (500 ng); 2) VMH lesion plus icv injection of saline; 3) sham lesion plus icv injection of PGE₁; and 4) sham lesion plus icv injection of saline. PGE₁ induced an increase in the firing rate of IBAT nerves and the colonic and IBAT temperatures. These effects were reduced by VMH lesion. The findings indicate that acute lesions of the VMH reduce the effects of PGE₁ and seem to suggest a possible role played by the VMH in the control of the sympathetic activation and the thermogenic changes during PGE₁ hyperthermia.     

Direct action of cGMP on the conductance of retinal rod plasma membrane

In order to identify the intracellular transmitter in the phototransduction process in the retinal rod, the action of cGMP, 2',3'cGMP, cAMP, GMP and Ca2+ on the isolated inside-out patches of the plasma membrane of retinal rods of the frog (Rana temporaria) was studied. cGMP applied at the intracellular membrane surface markedly increased the conductance of patches. The action of cGMP took place in the absence of nucleoside triphosphates and, hence, was not mediated by protein phosphorylation. The dependence of cGMP-induced component of conductance on cGMP concentration was S-shaped, with half-saturation within 10-30 microM and a Hill coefficient of about 1.7-1.8. cAMP, 2',3'cGMP, GMP (1 mM) did not exhibit any action on the membrane. Ca2+ did not affect the patch conductance in the absence of cGMP. In the presence of cGMP, lowering Ca2+ concentration from 10(-3) to 10(-8) M decreased the cGMP-dependent component of conductance by 20-30%. The approximate value of the elementary event underlying the cGMP-induced conductance estimated from the magnitude of the variance of the cGMP-induced current is within 100-250 fS. We suppose that the cGMP-activated channels found by us provide the light-sensitive conductance of the rod plasma membrane in vivo and that cGMP is the intracellular transmitter acting in the phototransduction process.     

Population structure in the American oyster as inferred by nuclear gene genealogies

Multiple haplotypes from each of three nuclear loci were isolated and sequenced from geographic populations of the American oyster, Crassostrea virginica. In tests of alternative phylogeographic hypotheses for this species, nuclear gene genealogies constructed for these haplotypes were compared to one another, to a mitochondrial gene tree, and to patterns of allele frequency variation in nuclear restriction site polymorphisms (RFLPs) and allozymes. Oyster populations from the Atlantic versus the Gulf of Mexico are not reciprocally monophyletic in any of the nuclear gene trees, despite considerable genetic variation and despite large allele frequency differences previously reported in several other genetic assays. If these populations were separated vicariantly in the past, either insufficient time has elapsed for neutral lineage sorting to have achieved monophyly at most nuclear loci, or balancing selection may have inhibited lineage extinction, or secondary gene flow may have moved haplotypes between regions. These and other possibilities are examined in light of available genetic evidence, and it is concluded that no simple explanation can account for the great variety of population genetic patterns across loci displayed by American oysters. Regardless of the source of this heterogeneity, this study provides an empirical demonstration that different sequences of DNA within the same organismal pedigree can have quite different phylogeographic histories.      

植物抗病基因工程进展(续)

植物抗病基因工程进展（续）洪剑明印莉萍邱泽生（首都师范大学生物系北京１０００３７）ＰＲＯＧＲＥＳＳＯＦＧＥＮＥＴＩＣＥＮＧＩＮＥＥＲＩＮＧＦＯＲＰＬＡＮＴＤＩＳＥＡＳＥＲＥＳＩＳＴＡＮＣＥＨＯＮＧＪｉａｎＭｉｎｇＹＩＮＬｉＰｉｎｇＱＩＵＺｅＳｈ...