Optimization of speed and accuracy of decoding in translation

The speed and accuracy of protein synthesis are fundamental parameters for understanding the fitness of living cells, the quality control of translation, and the evolution of ribosomes. In this study, we analyse the speed and accuracy of the decoding step under conditions reproducing the high speed of translation in vivo. We show that error frequency is close to 10⁻³, consistent with the values measured in vivo. Selectivity is predominantly due to the differences in k_cat values for cognate and near-cognate reactions, whereas the intrinsic affinity differences are not used for tRNA discrimination. Thus, the ribosome seems to be optimized towards high speed of translation at the cost of fidelity. Competition with near- and non-cognate ternary complexes reduces the rate of GTP hydrolysis in the cognate ternary complex, but does not appreciably affect the rate-limiting tRNA accommodation step. The GTP hydrolysis step is crucial for the optimization of both the speed and accuracy, which explains the necessity for the trade-off between the two fundamental parameters of translation.     

The role of challenging incentives in feedback-assisted heart rate reduction for coronary-prone adult males

Three experiments were performed to study the influence of challenging incentives on feedback-assisted heart rate reduction for coronary-prone (Type A) and non-coronary-prone (Type B) males. In the first experiment, when subjects were given a competitive instructional set, Type As were significantly more successful relative to Type Bs in reducing their heart rate; with a noncompetitive set, Type Bs were significantly more successful than were Type As. In the second experiment, when told that heart rate reduction was a scarce ability, Type As reduced heart rate significantly better than did Type Bs; when told that heart rate reduction was a common ability, Type Bs achieved significantly greater heart rate reduction than did Type As. In the third experiment, when heart rate reduction was described as being instrumental to time-urgency (i.e., getting more done in less time), Type As reduced heart rate significantly bettern than did Type Bs; when heart rate reduction was described as being instrumental to relaxation, Type Bs were significantly better able to reduce heart rate. In all three studies, the incentives had no effect on heart rate when feedback was not provided. The results are discussed as support for the notion that Type A behavioral pattern characteristics can be exploited to reduce Type A symptoms. Implications for how coronary-prone individuals may be challenged to modify symptoms within the clinical setting are discussed.     

Comparison of 60-Hz electric fields and incandescent light as aversive stimuli controlling the behavior of rats

Rats were exposed to two procedures which enabled them to press a lever to turn off a 90 or 100 kV/m 60-Hz electric field or, later in the study, illumination from an incandescent lamp. Under one procedure, a response turned off the stimulus for a fixed duration, after which the stimulus was turned on again. A response during the off-period restarted the fixed duration. None of the rats turned the field off reliably. Next, under an alternative procedure, pressing one lever turned the field off; pressing the other lever turned it back on; responding under those conditions differed little from that seen at 0 kV/m. Under both procedures, when illumination from an incandescent lamp served as the stimulus, each rat did turn the stimulus off, and performances varied with stimulus intensity. The results show that a 100 kV/m 60-Hz electric field is not sufficient to function as an aversive stimulus under two procedures where illumination from a lamp does function as an aversive stimulus.     

Fibroblast growth factor signaling in Caenorhabditis elegans.

Growth factor receptor tyrosine kinases (RTKs), such as the fibroblast growth factor receptor (FGFR), play a major role in how cells communicate with their environment. FGFR signaling is crucial for normal development, and its misregulation in humans has been linked to developmental abnormalities and cancer. The precise molecular mechanisms by which FGFRs transduce extracellular signals to effect specific biologic responses is an area of intense research. Genetic analyses in model organisms have played a central role in our evolving understanding of these signal transduction cascades. Genetic studies in the nematode C. elegans have contributed to our knowledge of FGFR signaling by identifying genes involved in FGFR signal transduction and linking their gene products together into signaling modules. This review will describe FGFR-mediated signal transduction in C. elegans and focus on how these studies have contributed to our understanding of how FGFRs orchestrate the assembly of intracellular signaling pathways.     

Evaluation of N2-fixation and nitrogen economy of a maize/cowpea intercrop system using15N dilution methods

Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha⁻¹, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N₂ fixation of sole or intercrop cowpea (1984/85 season) based on the¹⁵N natural abundance and¹⁵N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N₂-fixation, with N₂-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N₂-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N₂-fixation was estimated tobe 59 kg N ha⁻¹ in the plots receiving no fertilizer N, and 73 kg N ha⁻¹ in plots receiving 25 kg N ha⁻¹ as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha⁻¹ respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.     

Class I-like MHC molecules expressed by baboon placental syncytiotrophoblast

Human placental villous trophoblast is known to be unreactive with W6/32 and other monoclonal antibodies recognizing monomorphic determinants of human class I MHC heavy chains, whereas extravillous cytotrophoblast in the placental bed is W6/32-reactive by immunohistology. We have now demonstrated, in contrast, that syncytiotrophoblast is the only cellular component of baboon early placental villous tissue which is reactive with any of these antibodies. Radioimmunoprecipitation of detergent-solubilized baboon placental membrane preparations, and subsequent SDS-PAGE, has shown the W6/32-reactive component to have an m.w. of 41,000 and to be associated with beta 2-microglobulin, whereas baboon peripheral lymphocytes express 45,000 m.w. W6/32-reactive antigens comparable with the HLA-A,B,C heavy chains of human lymphocytes.     

Regulation of transplasmalemma electron transport in oat mesophyll cells by sphingoid bases and blue light

Long-chain sphingoid bases inhibit transplasmalemma electron transport in certain animal cells in part by inhibiting protein phosphorylation. As a first step in determining whether similar regulatory processes exist for cell surface redox activity in plants, peeled leaf segments of Avena sativa L. cv Garry were exposed to sphingoid bases and other long chain lipids. Sphingoid bases which are the most active inhibitors of protein kinase C in animal cells inhibit transplasmalemma electron transport by mesophyll cells in the dark as measured by reduction of exogenous ferricyanide. In white light, however, the same compounds markedly stimulate redox activity. The stimulation by sphingoid bases in the light is not eliminated by the inhibitor of photosynthesis, 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU). Redox activity remaining in the presence of DCMU and sphingoid bases can be observed in blue but not red light. A tentative hypothesis considering the involvement of two separate redox systems is presented in an attempt of explain the disparate action of sphingoid bases on electron transport across the plasmalemma.