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PubMed2003

Bidirectional electron transfer in photosystem I: electron transfer on the PsaA side is not essential for phototrophic growth in Chlamydomonas.

We have used pulsed electron paramagnetic resonance (EPR) measurements of the electron spin polarised (ESP) signals arising from the geminate radical pair P700(z.rad;+)/A(1)(z.rad;-) to detect electron transfer on both the PsaA and PsaB branches of redox cofactors in the photosystem I (PSI) reaction centre of Chlamydomonas reinhardtii. We have also used electron nuclear double resonance (ENDOR) spectroscopy to monitor the electronic structure of the bound phyllosemiquinones on both the PsaA and PsaB polypeptides. Both these spectroscopic assays have been used to analyse the effects of site-directed mutations to the axial ligands of the primary chlorophyll electron acceptor(s) A(0) and the conserved tryptophan in the PsaB phylloquinone (A(1)) binding pocket. Substitution of histidine for the axial ligand methionine on the PsaA branch (PsaA-M684H) blocks electron transfer to the PsaA-branch phylloquinone, and blocks photoaccumulation of the PsaA-branch phyllosemiquinone. However, this does not prevent photoautotrophic growth, indicating that electron transfer via the PsaB branch must take place and is alone sufficient to support growth. The corresponding substitution on the PsaB branch (PsaB-M664H) blocks kinetic electron transfer to the PsaB phylloquinone at 100 K, but does not block the photoaccumulation of the phyllosemiquinone. This transformant is unable to grow photoautotrophically although PsaA-branch electron transfer to and from the phyllosemiquinone is functional, indicating that the B branch of electron transfer may be essential for photoautotrophic growth. Mutation of the conserved tryptophan PsaB-W673 to leucine affects the electronic structure of the PsaB phyllosemiquinone, and also prevents photoautotrophic growth.

Animals↗

PubMed2003

Have ATLS and national transfer guidelines improved the quality of resuscitation and transfer of head-injured patients? A prospective survey from a Regional Neurosurgical Unit.

High-quality resuscitation and care during transfer of head-injured patients is essential to prevent secondary brain injury. We have prospectively assessed the standard of resuscitation in 50 consecutive head-injured patients transferred to our unit, and compared our findings with previous studies performed before the advanced trauma life support course (ATLS) had become widespread and national guidelines on the transfer of head injuries had been produced by the Association of Anaesthetists of Great Britain and Ireland (AAGBI). Delays in transfer, management of the airway, adequate cervical spine assessment, hypoxia (P(a)O(2) <13 kPa), hypotension (systolic BP <90 mmHg), missed injuries and the experience of the medical escort were compared against the standards laid out in ATLS and AAGBI Guidelines. The mean, unavoidable delay from arrival at the local accident and emergency unit to arrival was 7.4+/-1.9h (mean+/-95%CI) with most of the delay being prior to initial referral. Two patients arrived with an unsecured airway with a GCS=8/15; 26 had inadequate cervical spine imaging; 7 patients arrived hypoxic and 2 patients arrived hypotensive; most of these insults occurred during the transfer. Forty-six percent of medical escorts did not fulfil the minimum standard of experience. ATLS and AAGBI guidelines have provided only modest improvements in patient care at the expense of long delays in transfer. The incidence of hypoxia and hypotension remains unacceptably high.

Adolescent↗

PubMed2000

High-density lipoprotein cholesterol esterification and transfer rates to lighter density lipoproteins mediated by cholesteryl ester transfer protein in the fasting and postprandial periods are not altered in type 1 diabetes mellitus.

Background: Diabetes mellitus is associated with atherosclerosis that has, in part, been ascribed to abnormalities in the reverse cholesterol transport system. Methods: We determined, in the fasting and post-alimentary periods, rates of HDL cholesterol esterification and transfer to apoB-containing lipoproteins, cholesteryl ester transfer protein (CETP) concentration, and apoB lipoprotein size in 10 type 1 diabetics and 10 well-matched controls. Autologous HDL was labeled with [14C]cholesterol and incubated at 37 degrees C during a period of 30 min for measurement of the cholesterol esterification rate (CER), as well as for 24 h for measurement of the endogenous HDL [14C]cholesteryl ester ([14C]CE) transfer rate to apoB-containing lipoproteins after 2- and 4-h incubations with the subject's own plasma. Exogenous cholesteryl ester transfer activity (CETA) was estimated by incubation of the participant's plasma (CETP source) with [14C]CE-HDL and VLDL from a pool of plasma donors. ApoB lipoprotein size was determined using non-denaturing polyacrylamide gradient gel electrophoresis of whole plasma. Results: Contrary to previous studies, we showed that even not well-controlled type 1 diabetics did not differ from lipid-matched, non-diabetic subjects in HDL-[14C]cholesterol esterification rate, transfer rates, or CETP concentration. CETP concentration correlates with the exogenous method of [14C]CE transfer and with the endogenous method only when the latter is corrected for plasma triacylglycerol (TG) concentration. In addition, during the postprandial phase, diabetic patients' VLDL are smaller and IDL size increases less than in controls. Conclusion: In type 1 diabetes mellitus, CETA is not altered when the plasma levels of donor and/or acceptor lipoproteins are within the normal range.

Journal Article↗

PubMed1998

Lipid transfer particle catalyzes transfer of carotenoids between lipophorins of Bombyx mori.

The yellow color of Bombyx mori hemolymph is due to the presence of carotenoids, which are primarily associated with lipophorin particles. Carotenoids were extracted from high density lipophorin (HDLp) of B. mori and analyzed by HPLC. HDLp contained 33 micrograms of carotenoids per mg protein. Over 90% of carotenoids were lutein while alpha-carotene and beta-carotene were minor components. When larval hemolymph was subjected to density gradient ultracentrifugation, a second minor yellow band was present, which was identified as B. mori lipid transfer particle (LTP). During other life stages examined however, this second band was not visible. To determine if coloration of LTP may fluctuate during development, we determined its concentration in hemolymph and compared it to that of lipophorin. Both proteins were present during all life stages and their concentrations gradually increased. The ratio of lipophorin: LTP was 10-15:1 during the fourth and fifth instar larval stages, and 20-30:1 during the pupal and adult stages. Thus, there was no correlation between the yellow color attributed to LTP and its hemolymph concentration. It is possible that yellow coloration of the LTP fraction corresponds to developmental stages when the particle is active in carotene transport. To determine if LTP is capable of facilitating carotene transfer, we took advantage of a white hemolymph B. mori strain which, when fed artificial diet containing a low carotene content, gives rise to a lipophorin that is nearly colorless. A spectrophotometric, carotene specific, transfer assay was developed which employed wild type, carotene-rich HDLp as donor particle and colorless low density lipophorin, derived from the white hemolymph strain animals, as acceptor particle. In incubations lacking LTP carotenes remained associated with HDLp while inclusion of LTP induced a redistribution of carotenes between the donor and acceptor in a time and concentration dependent manner. Time course studies suggested the rate of LTP-mediated carotene transfer was relatively slow, requiring up to 4 h to reach equilibrium. By contrast, studies employing 3H-diacylglycerol labeled HDLp as donor particle in lipid transfer assays revealed a rapid equilibration of label between the particles. Thus, it is plausible that the slower rate of LTP-mediated carotene transfer is due to its probable sequestration in the core of HDLp.

Animals↗

PubMed1991

Laser flash photolysis studies of the kinetics of electron-transfer reactions of Saccharomyces flavocytochrome b2: evidence for conformational gating of intramolecular electron transfer induced by pyruvate binding.

The kinetics of reduction of the flavocytochrome from Saccharomyces cerevisiae by exogenous deazaflavin semiquinones have been investigated by using laser flash photolysis. Direct reduction by deazaflavin semiquinone of both the b2 heme and the FMN cofactor occurred via second-order kinetics with similar rate constants (9 x 10(8) M-1 s-1). A slower, monoexponential, phase of FMN reoxidation was also observed, concurrent with a slow phase of heme reduction. The latter accounted for approximately 20-25% of the total heme absorbance change. Both of these slow phases were protein concentration dependent, yielding identical second-order rate constants (1.1 x 10(7) M-1 s-1), and were interpreted as resulting from intermolecular electron transfer from the FMN semiquinone on one protein molecule to an oxidized heme on a second molecule. Consistent with this conclusion, no slow phase of heme reduction was observed with deflavo-flavocytochrome b2. Upon the addition of pyruvate (but not D-lactate or oxalate), the second-order rate constant for heme reduction was unaffected, but direct reduction of the FMN cofactor was no longer observed. Reduction of the heme cofactor was followed by a slower partial reoxidation, which occurred concomitantly with a monoexponential phase of FMN reduction. Both processes were protein concentration independent and were interpreted as the result of intramolecular electron transfer from reduced b2 heme to oxidized FMN. Potentiometric titrations of the flavocytochrome in the absence and presence of pyruvate demonstrated that the thermodynamic driving force for electron transfer from FMN to heme is much greater in the absence of pyruvate. Despite this, intramolecular electron transfer was only observed in the presence of pyruvate. This result is interpreted in terms of a conformational change induced by pyruvate binding which permits electron transfer between the cofactors. The rate constant for intramolecular electron transfer in the presence of pyruvate was dependent on ionic strength, suggesting the occurrence of electrostatic effects which influence this process.

Electron Transport↗

PubMed1987

Mechanism of transfer of reduced nicotinamide adenine dinucleotide among dehydrogenases. Transfer rates and equilibria with enzyme-enzyme complexes.

The direct transfer of NADH between A-B pairs of dehydrogenases and also the dissociation of NADH from individual E-NADH complexes have been investigated by transient stopped-flow kinetic techniques. Such A-B transfers of NADH occur without the intermediate dissociation of coenzyme into the aqueous solvent environment [Srivastava, D.K., & Bernhard, S.A. (1985) Biochemistry 24, 623-628]. The equilibrium distributions of limiting NADH among aqueous solvent and A and B dehydrogenase sites have also been determined. At sufficiently high but realizable concentrations of dehydrogenases, both the transfer rate and the equilibrium distribution of bound NADH are virtually independent of the excessive enzyme concentrations; at excessive E2 concentration, substantial NADH is bound to the E1 site. These results further substantiate earlier kinetic arguments for the preferential formation of an EA-NADH-EB complex, within which coenzyme is directly transferred between sites. The unimolecular specific rates of coenzyme transfer from site to site are nearly invariant among different A-B dehydrogenase pairs. The equilibrium constants for the distribution of coenzyme within the EA X EB complexes are near unity. At high [E2] and for [E2] greater than [E1] greater than [NADH], E1-NADH X E2 and E1 X NADH-E2 are virtually the only coenzyme-contained species. In contrast to the nearly invariant unimolecular NADH transfer rates within EA X EB complexes, unimolecular specific rates of dissociation of NADH from E-NADH into aqueous solution are highly variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2002

Proton-coupled electron transfer versus hydrogen atom transfer in benzyl/toluene, methoxyl/methanol, and phenoxyl/phenol self-exchange reactions.

Degenerate hydrogen atom exchange reactions have been studied using calculations, based on density functional theory (DFT), for (i) benzyl radical plus toluene, (ii) phenoxyl radical plus phenol, and (iii) methoxyl radical plus methanol. The first and third reactions occur via hydrogen atom transfer (HAT) mechanisms. The transition structure (TS) for benzyl/toluene hydrogen exchange has C(2)(h)() symmetry and corresponds to the approach of the 2p-pi orbital on the benzylic carbon of the radical to a benzylic hydrogen of toluene. In this TS, and in the similar C(2) TS for methoxyl/methanol hydrogen exchange, the SOMO has significant density in atomic orbitals that lie along the C-H vectors in the former reaction and nearly along the O-H vectors in the latter. In contrast, the SOMO at the phenoxyl/phenol TS is a pi symmetry orbital within each of the C(6)H(5)O units, involving 2p atomic orbitals on the oxygen atoms that are essentially orthogonal to the O.H.O vector. The transferring hydrogen in this reaction is a proton that is part of a typical hydrogen bond, involving a sigma lone pair on the oxygen of the phenoxyl radical and the O-H bond of phenol. Because the proton is transferred between oxygen sigma orbitals, and the electron is transferred between oxygen pi orbitals, this reaction should be described as a proton-coupled electron transfer (PCET). The PCET mechanism requires the formation of a hydrogen bond, and so is not available for benzyl/toluene exchange. The preference for phenoxyl/phenol to occur by PCET while methoxyl/methanol exchange occurs by HAT is traced to the greater pi donating ability of phenyl over methyl. This results in greater electron density on the oxygens in the PCET transition structure for phenoxyl/phenol, as compared to the PCET hilltop for methoxyl/methanol, and the greater electron density on the oxygens selectively stabilizes the phenoxyl/phenol TS by providing a larger binding energy of the transferring proton.

Free Radicals↗

PubMed2003

Effects of hydrogen bonding on metal ion-promoted intramolecular electron transfer and photoinduced electron transfer in a ferrocene-quinone dyad with a rigid amide spacer.

A ferrocene-quinone dyad (Fc-Q) with a rigid amide spacer and Fc-(Me)Q dyad, in which the amide proton acting as a hydrogen-bonding acceptor is replaced by the methyl group, are employed to examine the effects of hydrogen bonding on both the thermal and the photoinduced electron-transfer reactions. The hydrogen bonding of the semiquinone radical anion with the amide proton in Fc-Q(.-) produced by the electron-transfer reduction of Fc-Q is indicated by the significant positive shift of the one-electron reduction potential of Fc-Q. The hyperfine coupling constants of Fc-Q(.-) also indicate the existence of hydrogen bonding, agreeing with those predicted by the density functional calculation. The hydrogen-bonding dynamics in the photoinduced electron transfer from the ferrocene (Fc) to the quinone moiety (Q) in Fc-Q have been successfully detected in the femtosecond laser flash photolysis experiments. Thermal intramolecular electron transfer from Fc to Q in Fc-Q and Fc-(Me)Q also occurs efficiently in the presence of metal ions in acetonitrile at 298 K. The hydrogen bond formed between the semiquinone radical anion and the amide proton in Fc-Q results in remarkable acceleration of the rate of metal ion-promoted electron transfer as compared to the rate of Fc-(Me)Q in which hydrogen bonding is prohibited. The metal ion-promoted electron-transfer rates are well correlated with the binding energies of superoxide ion-metal ion complexes, which are derived from the g(zz) values of the ESR spectra.

Amides↗

PubMed2004

Theoretical study of benzotriazole UV photostability: ultrafast deactivation through coupled proton and electron transfer triggered by a charge-transfer state.

A theoretical CASSCF study of the reaction path for excited-state intramolecular proton transfer (ESIPT) for a model system derived from the UV absorber 2-(2'-hydroxyphenyl) benzotriazole without the fused benzo ring on the triazole has been carried out. A planar reaction path can be optimized but is shown to have no physical significance. The true reaction path involves twisted geometries. Adiabatic proton transfer is triggered by a charge-transfer from the phenol to the triazole group, and is followed by radiationless decay at the keto form. Along the nonplanar reaction path, there is a coupled proton and electron transfer in a manner similar to tryptophan. This rationalizes unexpected experimental results on the effect of electron withdrawing substituent groups on the photostability. The coupled proton and electron transfer is followed by a barrierless relaxation in the ground state to recover the enol form. An alternative photostabilization pathway from a phenyl localized state has also been documented and is similar to the channel 3 decay pathway in benzene photochemistry. Additionally, a long-lived intermediate for a twisted intramolecular charge-transfer (TICT) state has been identified as the species potentially responsible for the increase of blue fluorescence in strongly polar media.

Journal Article↗

PubMed2006

Electronic structures of intermolecular charge-transfer states in fast electron transfers with tetrathiafulvalene donor. Thermal and photoactivation of [2 + 4] cycloaddition to o-chloranil acceptor.

Tetrathiafulvalene (TTF) spontaneously forms a series of unusual charge-transfer complexes with various quinonoid acceptors such as o-chloranil (CA) that show pronounced near-IR absorption (lambda(CT) = 1100 nm). The successful isolation of the corresponding [1 : 1] donor-acceptor complex from solution and X-ray crystallographic analysis at low temperatures reveal the polarized charge-transfer state: [TTF(q+),CA(q-)] with high degree of charge-transfer (q = 0.6), which is spectrally and crystallographically distinguished from the separate redox (ion-pair) state: [TTF(+*) + CA(-*) ]. The unique interconversion of charge-transfer and electron-transfer states is theoretically well-accommodated by Mulliken theory using semi-empirical valence-bond and molecular-orbital methodologies. Mechanistic implications are discussed of both the thermally activated and the photochemically promoted processes via fast (intracomplex) electron transfer followed by collapse of the adiabatic and the non-adiabatic (vibrationally-excited) ion-pairs, respectively, to the [2 + 4] cycloadduct of tetrathiafulvalene and o-chloranil.

Journal Article↗

PubMed2006

Charge separation and energy transfer in a caroteno-C60 dyad: photoinduced electron transfer from the carotenoid excited states.

We have designed and synthesized a molecular dyad comprising a carotenoid pigment linked to a fullerene derivative (C-C(60)) in which the carotenoid acts both as an antenna for the fullerene and as an electron transfer partner. Ultrafast transient absorption spectroscopy was carried out on the dyad in order to investigate energy transfer and charge separation pathways and efficiencies upon excitation of the carotenoid moiety. When the dyad is dissolved in hexane energy transfer from the carotenoid S(2) state to the fullerene takes place on an ultrafast (sub 100 fs) timescale and no intramolecular electron transfer was detected. When the dyad is dissolved in toluene, the excited carotenoid decays from its excited states both by transferring energy to the fullerene and by forming a charge-separated C.+ -C(60).- . The charge-separated state is also formed from the excited fullerene following energy transfer from the carotenoid. These pathways lead to charge separation on the subpicosecond time scale (possibly from the S(2) state and the vibrationally excited S(1) state of the carotenoid), on the ps time scale (5.5 ps) from the relaxed S(1) state of the carotenoid, and from the excited state of C(60) in 23.5 ps. The charge-separated state lives for 1.3 ns and recombines to populate both the low-lying carotenoid triplet state and the dyad ground state.

Carotenoids↗

PubMed2004

A theory of nonvertical triplet energy transfer in terms of accurate potential energy surfaces: the transfer reaction from pi,pi* triplet donors to 1,3,5,7-cyclooctatetraene.

Triplet energy transfer (TET) from aromatic donors to 1,3,5,7-cyclooctatetraene (COT) is an extreme case of "nonvertical" behavior, where the transfer rate for low-energy donors is considerably faster than that predicted for a thermally activated (Arrhenius) process. To explain the anomalous TET of COT and other molecules, a new theoretical model based on transition state theory for nonadiabatic processes is proposed here, which makes use of the adiabatic potential energy surfaces (PES) of reactants and products, as computed from high-level quantum mechanical methods, and a nonadiabatic transfer rate constant. It is shown that the rate of transfer depends on a geometrical distortion parameter gamma=(2g(2)/kappa(1))(1/2) in which g stands for the norm of the energy gradient in the PES of the acceptor triplet state and kappa(1) is a combination of vibrational force constants of the ground-state acceptor in the gradient direction. The application of the model to existing experimental data for the triplet energy transfer reaction to COT from a series of pi,pi(*) triplet donors, provides a detailed interpretation of the parameters that determine the transfer rate constant. In addition, the model shows that the observed decrease of the acceptor electronic excitation energy is due to thermal activation of C=C bond stretchings and C-C bond torsions, which collectively change the ground-state COT bent conformation (D(2d)) toward a planar triplet state (D(8h)).

Journal Article↗

PubMed1991

Factors differentiating hospital transfers from long-term care facilities with high and low transfer rates.

This paper examines the factors that account for differences among nursing homes in terms of the rates at which they transfer patients to hospitals. Data from nursing staff and charts were collected on the 286 most recent transfers from 10 nursing homes. Discriminant function analyses indicated that from relatively equivalent patient populations, high-rate facilities tended to transfer the more chronically ill, physically frail patients; patients with infection (a potentially treatable condition within the long-term care facility); and to make transfers because of lack of resources such as a lab and X-ray equipment. Lack of IV therapy, while a frequently cited primary nonmedical reason for transfer, did not discriminate between high- and low-transfer-rate facilities.

Female↗

PubMed2000

Co-transfer of plasmids in association with conjugative transfer of mupirocin or mupirocin and penicillin resistance in methicillin-resistant Staphylococcus aureus.

Two distinct strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated from patients in a dermatology ward were also resistant to mupirocin. The mupirocin resistance plasmids from both strains were indistinguishable by EcoRI and HindIII restriction digest analysis, except for the presence of genes apparently mediating penicillinase production in some transconjugants. Conjugative transfer of the plasmid mediating mupirocin resistance from one of these strains to a recipient S. aureus was accompanied in some cases by co-transfer of plasmids mediating resistance to tetracycline or erythromycin; in some instances a plasmid which possessed no apparent resistance markers was also transferred. The second strain demonstrated conjugative transfer of penicillin and mupirocin resistance as well as transfer of a plasmid mediating gentamicin resistance, but transfer of erythromycin resistance was not apparently plasmid-mediated.

Anti-Bacterial Agents↗

PubMed1990

Liquid-to-Gas Mass Transfer in Anaerobic Processes: Inevitable Transfer Limitations of Methane and Hydrogen in the Biomethanation Process.

Liquid-to-gas mass transfer in anaerobic processes was investigated theoretically and experimentally. By using the classical definition of k(L)a, the global volumetric mass transfer coefficient, theoretical development of mass balances in such processes demonstrates that the mass transfer of highly soluble gases is not limited in the usual conditions occurring in anaerobic fermentors (low-intensity mixing). Conversely, the limitation is important for poorly soluble gases, such as methane and hydrogen. The latter could be overconcentrated to as much as 80 times the value at thermodynamic equilibrium. Such overconcentrations bring into question the biological interpretations that have been deduced solely from gaseous measurements. Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen (up to 12 and 70 times the equilibrium values, respectively). Hydrogen mass transfer coefficients were obtained from the direct measurements of dissolved and gaseous concentrations, while carbon dioxide coefficients were calculated from gas phase composition and calculation of related dissolved concentration. Methane transfer coefficients were based on calculations from the carbon dioxide coefficients. From mass balances performed on a gas bubble during its simulated growth and ascent to the surface of the liquid, the methane and carbon dioxide contents in the gas bubble appeared to be controlled by the bubble growth process, while the bubble ascent was largely responsible for a slight enrichment in hydrogen.

Journal Article↗

PubMed1992

Role of the origin of transfer in termination of strand transfer during bacterial conjugation.

Conjugal transfer of the broad-host-range plasmid R1162 is initiated and terminated at the nic site within the 38-bp origin of transfer (oriT). Termination involves ligation of the transferred single strand by the plasmid-encoded MobA protein. Several different assays were used to identify the oriT DNA required for termination. For plasmids containing two oriTs, with transfer initiated at one and terminated at the other, the inverted repeat within oriT is important for termination. Deletion of the outer arm reduces the termination frequency; those terminations that do occur probably depend upon nicking at this oriT prior to transfer. The locations of second-site suppressor mutations indicate that base pairing between the arms of the inverted repeat is important for termination. In vitro, the inverted repeat is not required for specific cleavage of single-stranded DNA at nic, but competition experiments indicate that oriTs with the inverted repeat are preferentially cleaved. We propose that the function of the oriT inverted repeat is to trap the plasmid-encoded MobA protein at the end of a round of strand transfer, thus ensuring that the protein is available for the ligation step.

Bacterial Proteins↗

PubMed1992

Dissection of IncP conjugative plasmid transfer: definition of the transfer region Tra2 by mobilization of the Tra1 region in trans.

We constructed a transfer system consisting of two compatible multicopy plasmids carrying the transfer regions Tra1 and Tra2 of the broad-host-range IncP plasmid RP4. In this system, the plasmid containing the Tra1 region with the origin of transfer (oriT) was transferred, whereas additional functions essential for the conjugative process were provided from the Tra2 plasmid in trans. The Tra2 region, as determined for matings between Escherichia coli cells, maps between coordinates 18.03 and 29.26 kb of the RP4 standard map. The section of Tra2 required for mobilization of the plasmid RSF1010 (IncQ) and the propagation of bacteriophages Pf3 and PRD1 appears to be the same as that needed for RP4 transfer. Tra2 regions of RP4 (IncP alpha) and R751 (IncP beta) are interchangeable, facilitating mobilization of the plasmid carrying the RP4 Tra1 region. The transfer frequencies of both systems are similar. Transcription of Tra2 proceeds clockwise relative to the standard map of RP4 and is probably initiated at a promoter region located upstream of trbB (kilB). From this promoter region the trfA operon and the Tra2 operon are likely to be transcribed divergently. A second potential promoter has been located immediately upstream of trbB (kilB). Plasmids encoding the functional Tra2 region can only be maintained stably in host cells in the presence of the RP4 regulation region carrying the korA-korB operon or part of it. This indicates the involvement of RP4 key regulatory functions that apparently are active not only in the control of replication but also in conjugation.

Base Sequence↗

PubMed1964

GENE TRANSFER BY F' STRAINS OF ESCHERICHIA COLI. IV. EFFECT OF A CHROMOSOMAL DELETION ON CHROMOSOME TRANSFER.

Pittard, James (Yale University, New Haven, Conn.), and T. Ramakrishnan. Gene transfer by F' strains of Escherichia coli. IV. The effect of a chromosomal deletion on chromosome transfer. J. Bacteriol. 88:367-373. 1964.-Evidence is presented that in an F' strain of Escherichia coli. AB1206, the chromosomal region corresponding to the merogenote of F(14) is deleted. AB1206 differs from all other F' strains in its stability and in its relative inability to transfer chromosomal markers under conditions in which transfer of the merogenote occurs at a frequency of 100%. Its stability can be accounted for by the fact that the loss of the F merogenote, which contains approximately 10% of the genetic information of the cell, would be a lethal event. The failure of AB1206 to transfer chromosomal markers, except at very low frequencies, can be explained in terms of the crossover model proposed to explain chromosome transfer by F' strains, since the homologous chromosomal region is missing in this strain. The conclusion that the chromosomal region is deleted is strengthened by the finding that the different enzymes coded for by the genes on F(14) are present in AB1206 at the level found in haploid strains, but have double this activity in homozygous diploids carrying F(14).

Chromosomes↗