Summary The lambda Red recombination system works poorly among unreplicated gam+ lambda chromosomes in recA- cells compared to recA+ cells. Recombination is not enhanced in recA- recB-cells. Thus, the inability of Red to promote recombination in recA- replication-blocked cross is not due to the hypothetical destruction of recombination intermediates by the recB nuclease. This conclusion strengthens previous proposals that the products of the red genes can operate upon recombinational intermediates which require recA activity for their formation. 相似文献
Summary The recombinant forming ability of recB– or recC– strains of E. coli K12 is almost totally recovered in merozygotes which are heterozygous for a genetic locus denoted rac which is located five minutes clockwise from trp on the genetic map. This transient recovery phenomenon only occurs when the donor strain is rac+ (wild type) and the recipient strain is rac-. The recombinants derived from such crosses all have the normal phenotype characteristic of recB– (or recC–) strains, and they are almost always rac-. The results imply that the rac+ locus (or loci) is zygotically expressed and excised from the chromosome in a manner which is analogous to the zygotic induction of a prophage. 相似文献
Individual deletions of acs and aceA genes in E. coli B (BL21) showed little difference in the metabolite accumulation patterns but deletion of the ackA gene alone or together with pta showed acetic acid gradually accumulated to 3.1 and 1.7 g/l, respectively, with a minimal extended lag in bacterial growth
and a higher pyruvate formation. Single poxB deletion in E. coli B (BL21) or additional poxB deletion in the ackA-pta mutants did not change the acetate accumulation pattern. When the acetate production genes (ackA-pta-poxB) were deleted in E. coli B (BL21) acetate still accumulated. This may be an indication that perhaps acetate is not only a by-product of carbon metabolism;
it is possible that acetate plays also a role in other cellular metabolite pathways. It is likely that there are alternative
acetate production pathways. 相似文献
Ethanol-hypersensitive strains (ets mutants), unable to grow on media containing 6% ethanol, were isolated from a sample of mutagenized Schizosaccharomyces pombe wild-type cells. Genetic analysis of these ets strains demonstrated that the ets phenotype is associated with mutations in a large set of genes, including cell division cycle (cdc) genes, largely non-overlapping with the set represented by the temperature conditional method; accordingly, we isolated some ets non-ts cdc– mutants, which may identify novel essential genes required for regulation of the S. pombe cell cycle. Conversely, seven well characterized ts cdc– mutants were tested for their ethanol sensitivity; among them, cdc1–7 and cdc13–117 exhibited a tight ets phenotype. Ethanol sensitivity was also tested in strains bearing different alleles of the cdc2 gene, and we found that some of them were ets, but others were non-ets; thus, ethanol hypersensitivity is an allele-specific phenotype. Based on the single base changes found in each particular allele of the cdc2 gene, it is shown that a single amino acid substitution in the p34cdc2 gene product can produce this ets phenotype, and that ethanol hypersensitivity is probably due to the influence of this alcohol on the secondary and/or tertiary structure of the target protein. Ethanol-dependent (etd) mutants were also identified as mutants that can only be propagated on ethanol-containing media. This novel type of conditional phenotype also covers many unrelated genes. One of these etd mutants, etd1-1, was further characterized because of the lethal cdc– phenotype of the mutant cells under restrictive conditions (absence of ethanol). The isolation of extragenic suppressors of etd1-1, and the complementation cloning of a DNA fragment encompassing the etd1+ wild-type gene (or an extragenic multicopy suppressor) demonstrate that current genetic techniques may be applied to mutants isolated by using ethanol as a selective agent. 相似文献
Summary Nonsense codon suppressing lysogens of E. coli have been made using 80 psu
3+
-A2 and 80 psu
oc+
-A2, heat-sensitive amber and ochre suppressing derivatives, respectively, of bacteriophage 80. The various lysogens selected differ in strength of suppression as well as in heat sensitivity of suppressor function. Heat-resistant derivatives, some still carrying the A2 mutation, can be selected from the heat sensitive parents. Mapping expreiments indicate that the 80 derivatives integrate at the tyrTV locus, which contains two copies of tRNA
1Tyr
. The origin of the various suppressor phenotypes appears to be related to the great variety of distinctive recombination events possible either between the incoming tRNA
1Tyr
gene and the host copies, or among the three copies of this gene in the lysogens. 相似文献
Summary The inheritance of an extrakaryotic mutation conferring temperature-sensitive growth on nonfermentable substrates and a high frequency of mutation to rho– has been studied. Multifactorial crosses (rho+xrho+) involving this mutation T
8S
and mitochondrial mutations conferring resistance to chloramphenicol, erythromycin, oligomycin or paromomycin revealed: a) Mutation T
8S
is localized on the mitDNA, referring to a new gene locus TSM1. b) Locus TSM1 appears to be weakly linked to the locus PAR1 and to the loci RIB1 and RIB3 but unlinked to the locus OLI1. c) The position of TSM1 is between PAR1 and the two closely linked loci RIB1 and RIB3, OLI1 is outside and not linked to the segment PAR-TSM-RIB. d) Mutation T
8S
does not significantly influence the process of mitochondrial recombination and its control by the mitochondrial locus . 相似文献
A cotransport system for Na+, K+ and Cl? in Ehrlich cells is described. It is insensitive towards ouabain but specifically inhibited by furosemide and other ‘high ceiling’ diuretics at concentrations which do not affect other pathways of the ions concerned. As the furosemide-sensitive fluxes of these ions are not affected by changes in membrane potential, and as their complete inhibition by furosemide does not appreciably alter the membrane potential, they appear to be electrically silent. Application of the pulse-response methods in terms of irreversible thermodynamics reveals tight coupling between the furosemide-sensitive flows of Na+, K+ and Cl? ( close to unity for all three combinations) at a stoichiometry of 1 : 1 : 2. The site for each of the ions appears to be rather specific: K+ can be replaced by Rb+ but not by other cations tested whereas Cl? can be poorly replaced by Br? but not by NO3?, in contradistinction to the Cl?-OH? exchange system. The cotransport system appears to function in cell volume regulation as it tends to make the cell swell, thus counteracting the shrinking effect of the ouabain-sensitive (Na+, K+) pump.The experiments presented could not clarify whether the cotransport process is a primary or secondary active one; while incongruence between transport and conjugated driving force seems to indicate primary active transport, it is very unlikely that hydrolysis of ATP supplies energy for the transport process, since there is no stimulation of ATP turnover observable under operation of the cotransport system. 相似文献
A method for measuring the gas temperature in an oxygen plasma by spectroscopy of the electronic transition from the O2(b1Σ
g+
, v = 0) metastable state of molecular oxygen into the O2(X3Σ
g−
, v = 0) ground state is considered in detail. The method is verified experimentally for the plasma of dc glow discharge in pure
oxygen. It is shown that the gas temperature can be determined by analyzing high-resolution spectra of the P branch of this transition, no matter whether its fine structure (PP and PQ branches) is resolved or masked, provided that the rotational structure of the spectrum is resolved. The feasibility of the
method proposed in 1999 by P. Maco and P. Veis for determining the gas temperature from the ratio between the intensity maxima
of the R and P branches of the O2(b1Σ
g+
, v = 0) → O2(X3Σ
g−
, v = 0) transition in a poorly resolved spectrum was studied experimentally. It is shown that, in order to use this method,
it is necessary to know the spectrograph instrumental function. The effect of the spatial inhomogeneity of the temperature
and concentration of O2(b1Σ
g+
) molecules on the accuracy of integral (over the plasma volume) measurements of the gas temperature is investigated using
spatially resolved spectroscopy of the O2(b1Σ
g+
, v = 0) → O2(X3Σ
g−
, v = 0) transition. It is shown that precise measurements of the temperature require that the optical measurement system be
thoroughly adjusted in order for the temperature and concentration of the emitting particles to vary insignificantly over
the optically selected volume.
Original Russian Text ? S.M. Zyryanov, D.V. Lopaev, 2007, published in Fizika Plazmy, 2007, Vol. 33, No. 6, pp. 563–574. 相似文献
Summary Electron microscopy study shows that cytochalasin treatment of the mullet damages the microfilaments system in the apex of gill ionocytes: the microfilaments are reduced in number and shortened. Cytochalasin causes a reduction of transgill potential difference and an increase of the Na+ and Cl– blood concentration, of the diffusional water permeability of the gill, of the Na+ branchial influx and of Cl– efflux. The increase of the Na+ influx may result in a reduction of the Na+ net excretion flux compared to the control. The increased permeability in cytochalasin treated fish facilitates the Cl– entry probably leading to a reduction of the net Cl– excretion. The partial inhibition of the K+ dependent components of Na+ and Cl– effluxes also contributes to the reduction of Na+ and Cl– excretion. The role of microfilaments in the mechanisms of ionic excretion by the gill is discussed. 相似文献
The balance of K+, Na+, and Cl− fluxes across the cell membrane with the Na+/K+ pump, ion channels, and Na+K+2Cl− (NKCC) and Na+-Cl− (NC) cotransport was calculated to determine the mechanism of cell shrinkage in apoptosis. It is shown that all unidirectional
K+, Na+, and Cl− fluxes; the ion channel permeability; and the membrane potential can be found using the principle of the flux balance if
the following experimental data are known: K+, Na+, and Cl− concentrations in cell water; total Cl− flux; total K+ influx; and the ouabain-inhibited pump component of the Rb+(K+) influx. The change in different ionic pathways during apoptosis was estimated by calculations based on the data reported
in the preceded paper (Yurinskaya et al., 2010). It is found that cell shrinkage and the shift in ion balance in U937 cells
induced to apoptosis with 1 μM staurosporine occur due to the coupling of reduced pump activity with a decrease in the integral
permeability of Na+ channels, whereas K+ and Cl− channel permeability remains almost unchanged. Calculations show that only a small part of the total fluxes of K+, Na+, and Cl− account for the fluxes mediated by NKCC and NC cotransporters. Despite the importance of cotransport fluxes for maintaining
the nonequilibrium steady-state distribution of Cl−, they cannot play a significant role in apoptotic cell shrinkage because of their minority and cannot be revealed by inhibitors. 相似文献
Summary In seawater (SW)-adaptedMugil andFundulus, gill effluxes of Na+
and of Cl–
and the simultaneously recorded transgill potential (P.D.) differ according to whether they are measured in stressed or rested animals.In rested animals of the two species, transfer to Ringer's solution considerably reduces the P.D. but not
. InFundulus,
is also decreased. Transfer of the two species from SW to fresh water (FW) reduces
and
by 75 to 85% and leads to a large inversion of P.D. When K+ is added to FW, a gill depolarization occurs, as well as a large increase of
and
.These results suggest that: 1) the P.D. originates primarily from the diffusion of cations, the gill permeability to Na+ (
) being greater than that to Cl– (
), 2) a Cl–/Cl– exchange independent of P.D. is associated with the Cl– pump; 3) Cl– pump activity is linked to Na+/K+ exchange which in turn is associated to a Na+/Na+ exchange diffusion mechanism.In stressed individuals of the two species, the P.D. in SW, as well as the P.D. changes observed during transfer experiments, are considerably reduced. The decrease of
and
observed after transfer from SW to FW are also minimised. Changes are smaller inFundulus. The decrease of P.D. characterizing stressed animals may be at least in part due to a 3 to 4 fold increase of
which becomes equal to
in both species.As a result of stress, the K+-activated Na+ and Cl– excretion mechanisms are totally inhibited inFundulus and partially so inMugil.Stress response seems more intense inFundulus and recovery from stress faster inMugil. 相似文献
Na+, K+ and Cl? concentrations () and activities (), and mucosal membrane potentials () were measured in epithelial cells of isolated bullfrog (Rana catesbeiana) small intestine. Segments of intestine were stripped of their external muscle layers, and bathed (at 25°C and pH 7.2) in oxygenated Ringer solutions containing 105 mM Na+ and Cl? and 5.4 mM K+. Na+ and K+ concentrations were determined by atomic absorption spectrometry and Cl? concentrations by conductometric titration following extraction of the dried tissue with 0.1 M HNO3. 14C-labelled inulin was used to determine extracellular volume. was measured with conventional open tip microelectrodes, with solid-state Cl?-selective silver microelectrodes and and with Na+- and K+-selective liquid ion-exchanger microelectrodes. The average recorded was ?34 mV. , and were 51, 105 and 52 mM. The corresponding values for , and were 18, 80 and 33 mM. These results suggest that a large fraction of the cytoplasmic Na+ is ‘bound’ or sequestered in an osmotically inactive form, that all, or virtually all the cytoplasmic K+ behaves as if in free solution, and that there is probably some binding of cytoplasmic Cl?. significantly exceeds the level corresponding to electrochemical equilibrium across the mucosal and baso-lateral cell membranes. Earlier studies showed that coupled mucosal entry of Na+ and Cl? is implicated in intracellular Cl? accumulation in this tissue. This study permitted estimation of the steady-state transapical Na+ and Cl? electrochemical potential differences (Δμ̄Na and Δμ̄Cl). Δμ̄Na (?7000 J · mol?1; cell minus mucosal medium) was energetically more than sufficient to account for Δμ̄Cl (1000–2000 J · mol?1). 相似文献
Vanadium(V)-induced hydrolyses of triphosphates in aqueous solutions were initiated in two ways: (1) oxidizing vanadium(IV)-polyphosphate complexes to produce metastable vanadium(V) complexes; (2) forming VO2+-polyphosphate complexes by acidification of solutions of VO43? and polyphosphate to yield equilibrium mixtures of V(V), polyphosphate, and their complexes. Hydrolysis rates for the complexes formed at 40°C ? T ? 25°C follow the order V2PPPi = 2(VPPPi) ≌ (VO2) ATP ? V(PPPi)2 ≌ PPPi. The hydrolysis of (V(V))2(PPPi) was not very temperature sensitive; the activation enthalpy appears small and the activation entropy large and negative. Mechanistic studies reveal that requirements for the activated state in metal-ion-catalyzed hydrolysis of polyphosphates include monodentate polyphosphate ligated cis to H2O or OH? in the coordination sphere of the metal ion: 相似文献
Effects of Na+ and K+ on Ca2+ transport by sarcoplasmic reticulum vesicles were studied in a medium containing high Mg2+ and ATP (2mM) and low Ca2+ (0.44μM) concentrations. Under these conditions, Na+ and K+ inhibit Ca2+ uptake. ATPase activity and membrane phosphorylation by ATP. Since the concentrations of ATP and Ca2+ used are consistent with relaxation in vivo, the results suggest that under physiological resting conditions the Ca2+ pump of the sarcoplasmic reticulum operates below its maximal capacity. 相似文献
Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone essential for the establishment and maintenance of pregnancy. The α- and β-subunits of hCG are highly cross-linked internally by disulfide bonds that seem to stabilize the tertiary structures required for the noncovalent association of the subunits to generate hormonal activity. This paper describes the results of our studies on the role of the disulfide bonds of hCG-β in heterodimer formation with the α-subunit. Six disulfide peptides incorporating each of the six disulfide bonds of hCG-β were screened, along with their linear counterparts, for their ability to competitively inhibit the recombination of α- and β-subunits. The disulfide peptides Cys (9–57), Cys (34–88) and Cys (38–90) were found to inhibit the α/β recombination whereas the remaining three disulfide peptides viz. Cys (23–72), Cys (26–110) and Cys (93–100) did not exhibit any inhibition activity. Interestingly, none of the linear peptides could inhibit the α/β recombination. Results clearly demonstrate that the disulfide bonds Cys9–Cys57, Cys34–Cys88 and Cys38–Cys90 of the β-subunit of hCG are crucial for heterodimer formation with the α-subunit thus providing experimental confirmation of the conclusions from the crystal structure of the hormone. 相似文献