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PubMed1995

Differential short-term transduction efficiency of adult versus newborn mouse tissues by adenoviral recombinants.

We demonstrated different transduction efficiency in several major organs of the immature (newborn) versus mature (adult) mice using adenoviral recombinants containing expression cassettes for either firefly luciferase or bacterial beta-galactosidase reporter genes. The studied tissues included skeletal muscle, heart, brain, lung, kidney, and liver. The transduction efficiency in all tissues, especially skeletal muscle, was significantly less in adults than in newborns, with two exceptions. In the heart, transduction efficiency was the same in newborns and adults, while in brain, it was greater in the adult than in the newborn. The cited differences in transduction efficiencies between newborn and adult tissues applied approximately equally to both reporter genes. The alpha v integrin level showed the same trend as the transduction efficiency in all tissues, except the heart. Polymerase chain reaction showed a specific adenoviral product in proportion to the reporter gene expression in muscle, heart, and brain. The results of this study should be considered in designing gene therapy strategies in genetic diseases.

Adenoviridae↗

PubMed1998

Insulin-like growth factor (IGF)-I but not IGF-II promotes lean growth and feed efficiency in broiler chickens.

The efficacy of exogenous IGFs to stimulate growth and modulate protein and fat deposition was examined in a number of broiler chicken lines. From around 600 g body weight the chickens received a continuous infusion of vehicle (0.1 M acetic acid), human recombinant IGF-I or [Gly1]IGF-II at 300 microg/kg body weight per day, or a combined infusion of 150 microg/kg/day of each IGF for 2 weeks. Experiment 1 used commercial broiler female chickens and included measurements of nitrogen balance, Ntau-methylhistidine excretion and muscle protein synthesis rates. In Experiment 2 the same treatments were applied to three experimental lines of chickens selected for high food consumption (relatively fat), high food utilisation efficiency (relatively lean), or at random (control). IGF-I, but not IGF-II, significantly increased growth rate and food utilisation efficiency by around 10-15% in each experiment, an effect which was consistent across all genotypes. Nitrogen balance was significantly increased by IGF-I in Experiment 1 as was carcass nitrogen content in Experiment 2, indicating that the increased growth was in lean tissue. Carcass fat was consistently reduced in chickens receiving IGF-I and was related to the levels of circulating IGF-I (r2 = 0.30, P < 0.01) but not triiodothyronine. Protein synthesis rates were unaffected by treatment and could not account for increased growth rate. However, there was a significant reduction in Ntau-methylhistidine excretion indicating a reduced rate of muscle protein breakdown in IGF-I-treated chickens (1. 56%/day vs 2.05%/day for IGF-I-treated vs controls, P < 0.05). The efficiency of feed utilisation was inversely related to the rate of protein breakdown (r2 = 0.25, P < 0.01). In conclusion, these experiments are the first to report an enhancement of growth and food utilisation efficiency by broiler chickens receiving exogenous IGF-I. Our results show that IGF-I may be important in controlling the growth and efficiency of food utilisation of young chickens at least in part by modulating the rates of protein breakdown.

Animal Nutritional Physiological Phenomena↗

PubMed2002

Measuring agricultural sustainability in terms of efficiency: the case of Dutch sugar beet growers.

Sustainability embraces socio-economic and bio-ecological dimensions or attributes. This paper presents a conceptual framework for quantifying sustainability on the basis of efficiency theory commonly used in economics. The conceptual model is implemented using Data Envelopment Analysis (DEA). Sustainability is measured for a sample of Dutch sugar beet growers. The average technical efficiency was only 50%. A positive correlation was found between technical efficiency and sustainable efficiency. Differences in efficiency among farmers were persistent within and between years. We conclude that there is considerable scope for improving the sustainability of arable farming by better management.

Agriculture↗

PubMed1994

Correlation of translation efficiency with the decay of lacZ mRNA in Escherichia coli.

We isolated mutations in the leader of a ribosomal protein (r-protein)/lacZ fusion gene in Escherichia coli that caused the mRNA to be translated at efficiencies between < 1% and 62% of the rate of wild-type message. Using a subset of these mutants with translation efficiencies between 5% and 62%, we studied both physical and functional decay of the mRNA after rifampicin inhibition of transcription initiation. The decay of physically intact transcript was analyzed by gel electrophoresis of hybrid-selected messenger RNA segments. The output from the message was analyzed by measuring the synthesis rate of r-protein/lacZ fusion protein. Decay of physically intact message after rifampicin addition correlated with the translation efficiency, with the more active messengers being more stable. Different segments of the r-protein/lacZ fusion mRNA decayed with the same rate, indicating that there is no hyper-labile region in the transcript. The decay rate was also independent of the length of the segment probed, suggesting that the mRNA is not degraded by random attacks along the entire length of the molecule. Our results are consistent with an overall 5' to 3' degradation pathway. Surprisingly, the rate of fusion protein synthesis did not decrease immediately after rifampicin addition. Rather, a lag preceded the exponential decay phase; the length of this delay correlated with the translation efficiency, such that the lag increased with increasing efficiency of translation. We suggest that these lags indicate that mRNAs are normally competing for ribosomes during exponential growth and, after rifampicin addition, RNA molecules with longer physical half-lives are translated by ribosomes released from fast decaying messengers.

Base Sequence↗

PubMed1997

Sequence-dependent modulation of nucleotide excision repair: the efficiency of the incision reaction is inversely correlated with the stability of the pre-incision UvrB-DNA complex.

The UvrABC excinuclease is involved in the nucleotide excision repair (NER) pathway. Sequence-dependent differences in repair efficiency have been reported for many different lesions, and it is often suggested that sites with poor repair contribute to the occurrence of mutation hot spots. However, guanine bases modified by N-2-acetylaminofluorence (AAF) within the NarI site (5'-G1G2CG3CC-3') are incised by the UvrABC excinuclease with different efficiencies in a pattern not correlated with the potency of mutation induction. To gain insight into the mechanism of sequence-dependent modulation of NER, we analyzed the formation, the structure and the stability of UvrB-DNA pre-incision complexes formed at all three positions of the AAF-modified NarI site. We show that the efficiency of release of UvrA2 from specific UvrA2B-DNA complexes is sequence-dependent and that the efficiency of incision is inversely related to the stability of the pre-incision complex. We propose that the pre-incision complex, [UvrB-DNA], when formed upon dissociation of UvrA2, undergoes a conformational change (isomerization step) giving rise to an unstable but incision-competent complex that we call [UvrB-DNA]'. The [UvrB-DNA] complex is stable and unable to form an incision-competent complex with UvrC. As the release of UvrA2, this isomerization step is sequence-dependent. Both steps contribute to modulate NER efficiency.

2-Acetylaminofluorene↗

PubMed1999

The role of RNA pseudoknot stem 1 length in the promotion of efficient -1 ribosomal frameshifting.

The ribosomal frameshifting signal present in the genomic RNA of the coronavirus infectious bronchitis virus (IBV) contains a classic hairpin-type RNA pseudoknot that is believed to possess coaxially stacked stems of 11 bp (stem 1) and 6 bp (stem 2). We investigated the influence of stem 1 length on the frameshift process by measuring the frameshift efficiency in vitro of a series of IBV-based pseudoknots whose stem 1 length was varied from 4 to 13 bp in single base-pair increments. Efficient frameshifting depended upon the presence of a minimum of 11 bp; pseudoknots with a shorter stem 1 were either non-functional or had reduced frameshift efficiency, despite the fact that a number of them had a stem 1 with a predicted stability equal to or greater than that of the wild-type IBV pseudoknot. An upper limit for stem 1 length was not determined, but pseudoknots containing a 12 or 13 bp stem 1 were fully functional. Structure probing analysis was carried out on RNAs containing either a ten or 11 bp stem 1; these experiments confirmed that both RNAs formed pseudoknots and appeared to be indistinguishable in conformation. Thus the difference in frameshifting efficiency seen with the two structures was not simply due to an inability of the 10 bp stem 1 construct to fold into a pseudoknot. In an attempt to identify other parameters which could account for the poor functionality of the shorter stem 1-containing pseudoknots, we investigated, in the context of the 10 bp stem 1 construct, the influence on frameshifting of altering the slippery sequence-pseudoknot spacing distance, loop 2 length, and the number of G residues at the bottom of the 5'-arm of stem 1. For each parameter, it was possible to find a condition where a modest stimulation of frameshifting was observable (about twofold, from seven to a maximal 17 %), but we were unable to find a situation where frameshifting approached the levels seen with 11 bp stem 1 constructs (48-57 %). Furthermore, in the next smaller construct (9 bp stem 1), changing the bottom four base-pairs to G.C (the optimal base composition) only stimulated frameshifting from 3 to 6 %, an efficiency about tenfold lower than seen with the 11 bp construct. Thus stem 1 length is a major factor in determining the functionality of this class of pseudoknot and this has implications for models of the frameshift process.

Base Sequence↗

PubMed1999

Evidence for an RNA pseudoknot loop-helix interaction essential for efficient -1 ribosomal frameshifting.

RNA pseudoknots are structural elements that participate in a variety of biological processes. At -1 ribosomal frameshifting sites, several types of pseudoknot have been identified which differ in their organisation and functionality. The pseudoknot found in infectious bronchitis virus (IBV) is typical of those that possess a long stem 1 of 11-12 bp and a long loop 2 (30-164 nt). A second group of pseudoknots are distinguishable that contain stems of only 5 to 7 bp and shorter loops. The NMR structure of one such pseudoknot, that of mouse mammary tumor virus (MMTV), has revealed that it is kinked at the stem 1-stem 2 junction, and that this kinked conformation is essential for efficient frameshifting. We recently investigated the effect on frameshifting of modulating stem 1 length and stability in IBV-based pseudoknots, and found that a stem 1 with at least 11 bp was needed for efficient frameshifting. Here, we describe the sequence manipulations that are necessary to bypass the requirement for an 11 bp stem 1 and to convert a short non-functional IBV-derived pseudoknot into a highly efficient, kinked frameshifter pseudoknot. Simple insertion of an adenine residue at the stem 1-stem 2 junction (an essential feature of a kinked pseudoknot) was not sufficient to create a functional pseudoknot. An additional change was needed: efficient frameshifting was recovered only when the last nucleotide of loop 2 was changed from a G to an A. The requirement for an A at the end of loop 2 is consistent with a loop-helix contact similar to those described in other RNA tertiary structures. A mutational analysis of both partners of the proposed interaction, the loop 2 terminal adenine residue and two G.C pairs near the top of stem 1, revealed that the interaction was essential for efficient frameshifting. The specific requirement for a 3'-terminal A residue was lost when loop 2 was increased from 8 to 14 nt, suggesting that the loop-helix contact may be required only in those pseudoknots with a short loop 2.

Base Sequence↗

PubMed1998

Calibration of STUD+ parameters to achieve optimally efficient broadband adiabatic decoupling in a single transient

To provide the most efficient conditions for spin decoupling with least RF power, master calibration curves are provided for the maximum centerband amplitude, and the minimum amplitude for the largest cycling sideband, resulting from STUD+ adiabatic decoupling applied during a single free induction decay. The principal curve is defined as a function of the four most critical experimental input parameters: the maximum amplitude of the RF field, RFmax, the length of the sech/tanh pulse, Tp, the extent of the frequency sweep, bwdth, and the coupling constant, Jo. Less critical parameters, the effective (or actual) decoupled bandwidth, bweff, and the sech/tanh truncation factor, beta, which become more important as bwdth is decreased, are calibrated in separate curves. The relative importance of nine additional factors in determining optimal decoupling performance in a single transient are considered. Specific parameters for efficient adiabatic decoupling can be determined via a set of four equations which will be most useful for 13C decoupling, covering the range of one-bond 13C1H coupling constants from 125 to 225 Hz, and decoupled bandwidths of 7 to 100 kHz, with a bandwidth of 100 kHz being the requirement for a 2 GHz spectrometer. The four equations are derived from a recent vector model of adiabatic decoupling, and experiment, supported by computer simulations. The vector model predicts an inverse linear relation between the centerband and maximum sideband amplitudes, and it predicts a simple parabolic relationship between maximum sideband amplitude and the product JoTp. The ratio bwdth/(RFmax)2 can be viewed as a characteristic time scale, tauc, affecting sideband levels, with tauc approximately Tp giving the most efficient STUD+ decoupling, as suggested by the adiabatic condition. Functional relationships between bwdth and less critical parameters, bweff and beta, for efficient decoupling can be derived from Bloch-equation calculations of the inversion profile for a single sech/tanh pulse. Residual splitting of the centerband, normally associated with incomplete or inefficient decoupling, is not seen in sech/tanh decoupling and therefore cannot be used as a measure of adiabatic decoupling efficiency. The calibrated experimental performance levels achieved in this study are within 20% of theoretical performance levels derived previously for ideal sech/tanh decoupling at high power, indicating a small scope for further improvement at practical RF power levels. The optimization procedures employed here will be generally applicable to any good combination of adiabatic inversion pulse and phase cycle. Copyright 1998 Academic Press.

Journal Article↗

PubMed1997

Improving the efficiency of the genetic code by varying the codon length--the perfect genetic code.

The function of DNA is to specify protein sequences. The four-base "alphabet" used in nucleic acids is translated to the 20 base alphabet of proteins (plus a stop signal) via the genetic code. The code is neither overlapping nor punctuated, but has mRNA sequences read in successive triplet codons until reaching a stop codon. The true genetic code uses three bases for every amino acid. The efficiency of the genetic code can be significantly increased if the requirement for a fixed codon length is dropped so that the more common amino acids have shorter codon lengths and rare amino acids have longer codon lengths. More efficient codes can be derived using the Shannon-Fano and Huffman coding algorithms. The compression achieved using a Huffman code cannot be improved upon. I have used these algorithms to derive efficient codes for representing protein sequences using both two and four bases. The length of DNA required to specify the complete set of protein sequences could be significantly shorter if transcription used a variable codon length. The restriction to a fixed codon length of three bases means that it takes 42% more DNA than the minimum necessary, and the genetic code is 70% efficient. One can think of many reasons why this maximally efficient code has not evolved: there is very little redundancy so almost any mutation causes an amino acid change. Many mutations will be potentially lethal frame-shift mutations, if the mutation leads to a change in codon length. It would be more difficult for the machinery of transcription to cope with a variable codon length. Nevertheless, in the strict and narrow sense of coding for protein sequences using the minimum length of DNA possible, the Huffman code derived here is perfect.

Algorithms↗

PubMed2000

Increasing Cooperation in Prisoner's Dilemmas by Establishing a Precedent of Efficiency in Coordination Games.

Coordination games have multiple Nash equilibria (i.e., sets of strategies which are best responses to one another). In weak-link coordination games players choose a number 1-7. Their payoff is increasing in the minimum number (or weakest link) and decreasing in the difference between their number and the minimum. Choosing 7 is an efficient equilibrium because it gives everybody a higher payoff than any other coordinated choice. Higher-payoff equilibria are riskier, however, so the game expresses the tradeoff between group efficiency and personal risk present in many social and organizational settings. We tested whether choosing efficiently in a weak-link game increases cooperative play in a subsequent prisoner's dilemma (PD) game. This cross-game transfer resembles the transfer of cooperative norms in small firms (which are more like coordination games than PDs) as firms grow larger and become like PDs. In two experiments, if a group of players share a history of playing the weak-link game efficiently, that efficiency precedent can transfer to a subsequent PD game, improving the level of cooperativeness. The effect of transfer is much larger in magnitude (increasing cooperation from 15-30% to 71%) than the effects of most variables in previous PD studies. However, the transfer effect depends on descriptive similarity of strategies in the two games, since it largely disappears when the strategies are numbered differently in the weak-link game and the PD. Copyright 2000 Academic Press.

Journal Article↗

PubMed1996

Efficient circularization in Escherichia coli of linear plasmid multimers from Dictyostelium discoideum genomic DNA.

Transformation of Escherichia coli with Dictyostelium discoideum genomic DNA containing integrated shuttle vectors in multicopy, tandemly duplicated format resulted in the establishment of the linear plasmid molecules as circular monomeric replicons. The transformation efficiencies were comparable to those obtained with circular plasmid DNA and the recovered plasmids were free of deletions and rearrangements. Digestion of the genomic DNA prior to the transformation using restriction enzymes that cut within the inserted plasmids reduced the transformation efficiency dramatically and a high proportion of the recovered plasmids carried deletions. Our results provide evidence that the linear plasmid multimers cyclize in E. coli by homologous recombination in order to be established as autonomously replicated plasmids. The efficiency of recircularization was found to be independent of the recA gene product but dramatically reduced in the absence of recB recC or sbcB gene products. However, the paradoxically high efficiency of transformation with plasmid multimers of a recB recC sbcB mutant indicated the presence of an additional pathway for recombinational recircularization independent of these gene products. Unlike previous studies using as a DNA source linearized plasmid monomers and dimers that were created in vitro, the use of linear plasmid multimers integrated into the D. discoideum genome ensured that none of the E. coli transformants we obtained could be attributed to low levels of uncut circular plasmid molecules. The efficient recovery of the plasmid monomers faithfully reflects the structure of the insertion and thus provides a useful tool in the characterization of such plasmid insertions in the genome of D. discoideum.

Animals↗

PubMed2000

Identification of efficiently cleaved substrates for HIV-1 protease using a phage display library and use in inhibitor development.

The recognition sequences for substrate cleavage by aspartic protease of HIV-1 are diverse and cleavage specificities are controlled by complex interactions between at least six amino acids around the cleavage site. We have identified 45 efficiently cleaved peptide substrates of HIV-1 protease (PR) using substrate phage display, an approach that can elucidate both context-dependent and context-independent preferences at individual subsites of a protease substrate. Many of the selected peptides were cleaved more efficiently and had lower K(m) values than physiologically relevant substrates of HIV-1 PR. Therefore, mutations occurring in the cleavage sites of the Gag and Gag-pol polyproteins of HIV-1 could significantly lower the K(m) values to better compete against drugs for protease binding while maintaining cleavage rates necessary for viral replication. The most efficiently cleaved peptide substrate derived from these phage, Ac-GSGIF*LETSL-NH(2), was cleaved 60 times more efficiently and had a K(m) approximately 260 times lower than a nine-amino-acid peptide based on the natural reverse transcriptase/integrase cleavage site when assayed at pH 5.6, 0.2 M NaCl. The peptide substrates selected served as frameworks for synthesis of tight binding reduced amide inhibitors of HIV-1 PR. The results show that the most efficiently cleaved substrates serve as the best templates for synthesis of the tightest binding inhibitors. Thus, defining changes in substrate preferences for drug-resistant proteases may aid in the development of more efficacious inhibitors.

Amides↗

PubMed2001

Basic amino acid residues in the V3 loop of simian immunodeficiency virus envelope alter viral coreceptor tropism and infectivity but do not allow efficient utilization of CXCR4 as entry cofactor.

In contrast to human immunodeficiency viruses type 1 and type 2 (HIV-1 and HIV-2, respectively), simian immunodeficiency virus (SIVmac) rarely uses CXCR4 (X4) for efficient entry into target cells. Basic amino acid residues in the V3 loop of HIV Env allow efficient coreceptor utilization of X4. Therefore, we investigated if similar changes in the SIVmac Env protein also mediate a coreceptor switch from CCR5 (R5) to X4. Functional analysis revealed that none of eight SIVmac variants, containing V3 regions with an overall charge between +4 and +10, efficiently utilized X4 as entry cofactor. Nonetheless, these alterations had differential effects on SIV coreceptor tropism and on Env expression levels. A single amino acid substitution of L328R, located near the tip of the V3 loop, resulted in grossly reduced Env expression levels and impaired viral infectivity. Notably, additional basic residues restored efficient Env expression and virion incorporation but not infectivity. In comparison to the L328R mutation, changes of P334K and D337K had little disruptive effects on SIVmac entry and replication. Interestingly, mutation of L320K and P321R disrupted coreceptor usage of GPR15 but not R5. These changes also impaired SIVmac replication in peripheral blood mononuclear cells (PBMC) derived from a Delta32/Delta32 donor but not in R5-expressing human or simian PBMC. Our results show that positively charged amino acid residues in the V3 loop affect SIVmac coreceptor tropism and infectivity but do not allow efficient utilization of X4.

Amino Acid Sequence↗

PubMed2002

The primary nucleotide sequence of the bovine leukemia virus RNA packaging signal can influence efficient RNA packaging and virus replication.

Two RNA stem-loop structures in the gag gene have been implicated as representing the primary encapsidation (packaging) signal for bovine leukemia virus (BLV), a member of the Delta retrovirus of the Retroviridae. In this study, we conducted an analysis of these RNA structures, stem loop 1 (SL1) and stem loop 2 (SL2), to determine if both the loop and the stem nucleotide bases are important for RNA encapsidation. We have found that the primary sequence of the unpaired bases located in the loop regions of both SL1 and SL2 are important for efficient RNA encapsidation and virus replication. The primary sequence of the bases that form the stems for both SL1 and SL2 was observed to aid in efficient encapsidation and replication. We also observed that the order of SL1 and SL2 is important for RNA encapsidation and virus replication efficiency. A viral RNA with two copies of either SL1 or SL2 was found to replicate and package RNA as efficiently as a viral RNA with only one copy of SL1 or SL2. This provides evidence that SL1 and SL2 are not functionally equivalent. Sequences from human T cell leukemia virus type 1 (HTLV-1) that are located in the same region of HTLV-1 as the SL1 and SL2 of BLV were used to replace the BLV SL1, SL2, or both in a BLV RNA. These BLV RNAs were still encapsidated and replicated, suggesting that these sequences may function as an encapsidation signal in HTLV-1. The chimeric RNAs did not replicate as well as the parental, indicating that the primary nucleotide sequence along with the secondary and tertiary structure of the RNA plays a role in efficient RNA encapsidation and replication.

Animals↗

PubMed1994

Addition of A- and U-rich sequence increases the splicing efficiency of a deleted form of a maize intron.

Plant introns are generally short (< 200 nt) and AU-rich, and an elevated AU content is necessary for efficient splicing. Further, an intron in some plant genes enhances gene expression by a post-transcriptional mechanism that results in an increase of cytoplasmic mRNA. The specific intron features responsible for efficient splicing and enhancement are not well characterized in plants. Internal deletions of up to 80% of two maize introns, Adh1 intron 1 and maize actin 3, indicate that large segments of these introns are dispensable for normal function. However, extensive deletion (> 75%) of Adh1 intron 1 diminishes both intron enhancement and splicing efficiency. This finding suggests that there are internal sequence motifs required for intron function, and that these motifs are redundant. We attempted to repair a deletion-impaired Adh1 intron 1 variant by adding back either oligomers of defined sequence content or fragments of maize internal intron sequence. The addition of AU-rich oligomers improved splicing efficiency and in one example, a U-rich oligomer activated a cryptic 3' splice acceptor. We also found that replacing the region proximal to the Adh1 intron 1 3' acceptor with U-rich sequence improved splicing. We found that adding G- and C-rich oligomers did not improve intron function, but a C-rich oligomer activated a cryptic 3' acceptor. The addition of internal intron sequence to an impaired intron improved splicing, and in one case, resulted in the activation of a cryptic 3' acceptor. We present evidence that U-rich sequence immediately upstream of the 3' splice junction increases splicing efficiency and contributes to, but does not uniquely specify, 3' acceptor AG choice.

Adenine↗

PubMed1992

Efficiency of labelling of red blood cells with technetium-99m after dipyridamole infusion for thallium-201 stress testing.

Experimental studies have suggested that dipyridamole may inhibit red blood cell labelling with technetium-99m. To evaluate whether this effect is clinically relevant to the performance of radionuclide ventriculography after dipyridamole-thallium stress testing, in vitro red blood cell labelling was compared immediately before and after thallium-201 stress scintigraphy combined with either dipyridamole infusion (30 patients) or exercise stress (20 patients). Modified in vivo red blood cell labelling efficiency was assessed in a further 36 patients following dipyridamole infusion and was compared with that in 15 patients following exercise stress. The importance of a reversal of the dipyridamole effects by aminophylline was evaluated for in vitro and modified in vivo techniques. The red blood cell labelling efficiency was not significantly different in patients following dipyridamole compared with that obtained following exercise stress for both in vitro (93% +/- 4% versus 91% +/- 4%) and modified in vivo (87% +/- 19% versus 90% +/- 6%) techniques. Also, in vitro red blood cell labelling efficiency after dipyridamole was not different to that before stress testing (93% +/- 4% versus 92% +/- 4%). Reversal with aminophylline had no significant effect on the in vitro labelling efficiency with either the in vitro technique (94% +/- 3% with reversal versus 92% +/- 5% without) or the modified in vivo technique (91% +/- 4% with reversal versus 82% +/- 26% without). These results suggest that the red blood cell labelling efficiency is not compromised by the preceding dipyridamole-thallium stress testing but can be optimised by using in vitro labelling.

Aged↗

PubMed1990

High efficiency transformation of Salmonella typhimurium and Salmonella typhi by electroporation.

Salmonella typhimurium and S. typhi were transformed with high efficiency by electroporation. Transformation efficiencies of up to 10(10) transformants per microgram of pBR322 were obtained. In contrast to chemical transformation methods, neither the smooth lipopolysaccharide of S. typhimurium nor the Vi capsular polysaccharide of S. typhi greatly affected transformation efficiency. The introduction of a ga1E mutation slightly improved transformation efficiency in S. typhimurium (less than tenfold) while the Vi antigen of S. typhi had no detectable effect. The transformation efficiency of S. typhimurium with DNA derived from Escherichia coli was increased greatly by the removal of the hsd restriction system (100-fold). Under these conditions electroporation can be used for the routine and direct transformation of Salmonella strains with partially purified (alkaline lysis) plasmid DNA from E. coli.

Antigens, Bacterial↗

PubMed1985

Efficiency of sweat evaporation in unacclimatized man working in a hot humid environment.

A method is devised where evaporation and dripping sweat rates can be continuously determined during work. 6 unacclimatized men performed work on a bicycle ergometer at 3 different workloads and in 3 humidities. Ambient temperatures were always equal to mean skin temperatures, thus eliminating all sensible heat transfer. Evaporation rates ranged between 6.8 and 11.2 g X min-1. Rates of dripping sweat ranged from a mean of 2.2 to 10.4 g X min-1. One subject dripped 20.3 g X min-1 in condition H3 (70% RH, 100 W). The fully wet skin in condition H3 corresponded to an evaporative heat transfer coefficient of 99 W X m-2 kPa. Efficiency of sweating, defined as the ratio between secreted and evaporated sweat, ranged from 87 (50% RH, 50 W) to 51% (70% RH, 100 W). Corresponding values of wettedness were 0.56 and 1.0. Efficiency fell to 51% for fully wet skin (H3), and in some subjects the efficiency values were remarkably low. One subject displayed an efficiency of 31% in condition H3. The reduction in efficiency at a given level of wettedness was higher than previously reported.

Acclimatization↗