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.     

Priming in the Type I-F CRISPR-Cas system triggers strand-independent spacer acquisition,bi-directionally from the primed protospacer

Clustered regularly interspaced short palindromic repeats (CRISPR), in combination with CRISPR associated (cas) genes, constitute CRISPR-Cas bacterial adaptive immune systems. To generate immunity, these systems acquire short sequences of nucleic acids from foreign invaders and incorporate these into their CRISPR arrays as spacers. This adaptation process is the least characterized step in CRISPR-Cas immunity. Here, we used Pectobacterium atrosepticum to investigate adaptation in Type I-F CRISPR-Cas systems. Pre-existing spacers that matched plasmids stimulated hyperactive primed acquisition and resulted in the incorporation of up to nine new spacers across all three native CRISPR arrays. Endogenous expression of the cas genes was sufficient, yet required, for priming. The new spacers inhibited conjugation and transformation, and interference was enhanced with increasing numbers of new spacers. We analyzed ∼350 new spacers acquired in priming events and identified a 5′-protospacer-GG-3′ protospacer adjacent motif. In contrast to priming in Type I-E systems, new spacers matched either plasmid strand and a biased distribution, including clustering near the primed protospacer, suggested a bi-directional translocation model for the Cas1:Cas2–3 adaptation machinery. Taken together these results indicate priming adaptation occurs in different CRISPR-Cas systems, that it can be highly active in wild-type strains and that the underlying mechanisms vary.     

Changes in responsiveness to ethylene and gibberellin during corolla expansion ofIpomoea nil

Corolla expansion inIpomoea nil appears to be triggered by changes in gibberellin concentration and ethylene production during development. We investigated the role of responsiveness to GA and ethylene in corolla expansion. The effects of growth regulators applied in vitro were measured as a change in area of corolla segments from younger (15–17 mm) and older (18–20 mm) whole corollas. Applied gibberellic acid (GA₃) significantly (p < 0.05) promoted growth in the younger segments but was less effective in the older segments. Moreover, applications of the GA biosynthesis inhibitors, PP333 (paclobutrazol) AMO₁₆₁₈ (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride), chlorocholine chloride, and tetcyclasis had little effect on younger segments but inhibited growth of older segments. The older corollas have apparently synthesized and accumulated enough GA-like substances to become less responsive to additional applied GA₃. The amount of growth induced by applied or endogenous GA depended on the amount of ethylene simultaneously produced in the tissue. The younger corollas rapidly produced ethylene from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and did not respond to applied ACC whereas the older corollas naturally produced much less ethylene and were significantly (p < 0.05) inhibited by applied ACC. When ethylene production was inhibited by applying aminoethoxyvinylglycine (AVG), growth was promoted in all segments. However, only the growth of the younger segments was further stimulated by simultaneously applied AVG and GA₃ over the GA₃ control. Thus the differential responses of segments from 15- to 20-mm long corollas to applied growth regulators reflect developmental changes in responsiveness of the developing corolla. The change in responsiveness is attributed in part to the changes in production of endogenous growth regulators and to the effect of one endogenous plant growth regulator (PGR) on the responsiveness of the corolla to another PGR.     

Pericentric inversion of chromosome 19 in three families

Summary Pericentric inversion of chromosome 19 has been found in several members of three unrelated families from a restricted geographical region. In one of the families, an additional pericentric inversion of chromosome 9 was observed. Reproductive problems, multiple abortions in two families and a neonatal death in the third, were present. A review of previously described cases is included, and the genetic risk connected with this type of rearrangement is also discussed.     

Initial reactions in the mineralization of 2-sulfobenzoate by Pseudomonas sp. RW611

Abstract Pseudomonas sp. strain RW611 utilized the ammonium salt of 2-sulfobenzoate as sole source of carbon, sulfur, nitrogen, and energy. The xenobiotic sulfo substituent was dioxygenolytically eliminated as sulfite, which was then slowly oxidized to sulfate. 2,3-Dihydroxybenzoate, which resulted from desulfonation underwent meta -cleavage, mediated by 2,3-dihydroxybenzoate 3,4-dioxygenase activity. This enzyme was inhibited by 3-chlorocatechol and 2,3,4-trihydroxybenzoate.     

Guidelines for selective radiological assessment of inversion ankle injuries.

A prospective study was performed to establish definitive guidelines for selective use of radiography in the assessment of inversion ankle injuries. Five hundred patients were included, representing 3.2% of the workload of the department during the study period. There were 379 soft tissue injuries, 56 malleolar fractures, 40 avulsion fractures, 21 fractures at the base of the fifth metatarsal, and four calcaneal fractures. Multiple logistic regression identified distal fibular tenderness, age, and ability to bear weight as the most important clinical variables in predicting important fractures (p less than 0.001). A policy of requesting x ray examination of only those patients with distal fibular tenderness or inability to bear weight or aged over 60, with a further proviso that no foot radiographs should be obtained, would produce a 60% reduction in ankle radiography in this centre without detriment to patient care.     

Bone mechanical properties after exercise training in young and old rats

The effects of a 10-wk training regimen on the mechanical properties of the femur and humerus were evaluated in 2.5- and 25-mo-old Fischer 344 female rats. The rats trained on a rodent treadmill 5 days/wk for 10 wk. Duration, grade, and speed increased until the rats maintained 1 h/day at 15% grade and either 15 m/min (old rats) or 36 m/min (young rats). Excised bones were mechanically tested with a 3-point flexure test for mechanical properties of force, stress, and strain. Fat-free dry weight (FFW) and moment of inertia were also obtained. With aging, similar increases were observed in both the femur and humerus for FFW, moment of inertia, and force. Ultimate stress was reduced in the senescent femur while strain was elevated; a similar but nonsignificant trend was observed in the humerus. Irrespective of age, training increased FFW in the femur and, to a lesser degree, in the humerus. Breaking force was elevated for both bones after training. In young and old bones, the training-induced differences in bone mass and force were similar, despite differences in training intensity. In the old trained rats, femur ultimate stress was greater than that in control rat femurs and similar to that in young rat femurs. The results of the present study indicate that training effects were not limited by age.