Reduced Amino Acid Specificity of Mammalian Tyrosyl-tRNA Synthetase Is Associated with Elevated Mistranslation of Tyr Codons

Quality control operates at different steps in translation to limit errors to approximately one mistranslated codon per 10,000 codons during mRNA-directed protein synthesis. Recent studies have suggested that error rates may actually vary considerably during translation under different growth conditions. Here we examined the misincorporation of Phe at Tyr codons during synthesis of a recombinant antibody produced in tyrosine-limited Chinese hamster ovary (CHO) cells. Tyr to Phe replacements were previously found to occur throughout the antibody at a rate of up to 0.7% irrespective of the identity or context of the Tyr codon translated. Despite this comparatively high mistranslation rate, no significant change in cellular viability was observed. Monitoring of Phe and Tyr levels revealed that changes in error rates correlated with changes in amino acid pools, suggesting that mischarging of tRNA^Tyr with noncognate Phe by tyrosyl-tRNA synthetase was responsible for mistranslation. Steady-state kinetic analyses of CHO cytoplasmic tyrosyl-tRNA synthetase revealed a 25-fold lower specificity for Tyr over Phe as compared with previously characterized bacterial enzymes, consistent with the observed increase in translation error rates during tyrosine limitation. Functional comparisons of mammalian and bacterial tyrosyl-tRNA synthetase revealed key differences at residues responsible for amino acid recognition, highlighting differences in evolutionary constraints for translation quality control.     

Mobilization and exudation of photo-assimilated14C by developing pods of groundnut (Arachis hypogaea L.)

Summary ‘Pod washings’ were collected from groundnut at three hour intervals for 24 hours after feeding the plants with¹⁴CO₂. Low radioactivity was found in the first four ‘Pod washings’ of 10 day old pods and the radioactivity increased with time. Highest radioactivity was found in washings of 20 and 30 day old pods and was twice the activity found in the washings of 50 day old pods. The radioactivity of both ethanol-soluble and insoluble fractions in pods was determined. The radioactivity mobilized into the pods increased with age and it was highest in 50 day old pods. The influence of the pod exudates on geocarposphere microflora during pod development is discussed.     

Convolutional neural network‐based malaria diagnosis from focus stack of blood smear images acquired using custom‐built slide scanner

The present paper introduces a focus stacking‐based approach for automated quantitative detection of Plasmodium falciparum malaria from blood smear. For the detection, a custom designed convolutional neural network (CNN) operating on focus stack of images is used. The cell counting problem is addressed as the segmentation problem and we propose a 2‐level segmentation strategy. Use of CNN operating on focus stack for the detection of malaria is first of its kind, and it not only improved the detection accuracy (both in terms of sensitivity [97.06%] and specificity [98.50%]) but also favored the processing on cell patches and avoided the need for hand‐engineered features. The slide images are acquired with a custom‐built portable slide scanner made from low‐cost, off‐the‐shelf components and is suitable for point‐of‐care diagnostics. The proposed approach of employing sophisticated algorithmic processing together with inexpensive instrumentation can potentially benefit clinicians to enable malaria diagnosis.      

Evaluation of the rate-limiting steps in the pathway of glucose metabolism in kidney cortex of normal, diabetic, cortisone-treated and growth hormone-treated rats

1. The activities of gluconeogenic and glycolytic enzymes and the concentrations of citrate, ammonia, amino acids, glycogen, glucose 6-phosphate, acetyl-CoA, lactate and pyruvate were measured in kidney cortex of normal, diabetic, cortisone-treated and growth hormone-treated rats. 2. In kidney cortex of diabetic, cortisone-treated and growth hormone-treated rats the activities of glucose 6-phosphatase (EC 3.1.3.9), fructose 1,6-diphosphatase (EC 3.1.3.11) and phosphopyruvate carboxylase (EC 4.1.1.32) were increased. 3. The activities of glutamate dehydrogenase (EC 1.4.1.3), alanine aminotransferase (EC 2.6.1.2), aspartate aminotransferase (EC 2.6.1.10) and pyruvate carboxylase (EC 6.4.1.1) were increased in diabetic and cortisone-treated rats. In growth hormone-treated rats the activity of aspartate aminotransferase was depressed but those of the other three enzymes were unchanged. 4. The activity of hexokinase (EC 2.7.1.1) was not altered in any of these conditions. Phosphofructokinase (EC 2.7.1.11) activity was depressed only in growth hormone-treated rats. Pyruvate kinase (EC 2.7.1.40) activity was depressed in cortisone-treated and growth hormone-treated rats but unchanged in diabetic rats. 5. Amino acids, acetyl-CoA and glucose 6-phosphate contents were increased in rat kidneys in all these three conditions. Ammonia content was increased in diabetic and cortisone-treated rats but was markedly diminished in growth hormone-treated rats. 6. The [lactate]/[pyruvate] ratio was elevated in diabetic and cortisone-treated rats but unchanged in growth hormone-treated rats. Citrate content was increased in the kidney cortex of diabetic and growth hormone-treated rats but was unchanged in cortisone-treated rats. The activity of ATP citrate lyase (EC 4.1.3.8) was depressed in diabetic and growth hormone-treated rats but was increased in cortisone-treated rats. 7. Glycogen content was moderately elevated in growth hormone-treated rats and markedly elevated in diabetic rats, whereas no change in glycogen content was observed in cortisone-treated rats. Glycogen synthetase (EC 2.4.1.11) activity was unchanged in all these three conditions. Phosphorylase (EC 2.4.1.1) activity was not affected in cortisone-treated rats but was depressed in diabetic and growth hormone-treated rats.     

Substituent activity relationship studies on new azolo benzoxazepinyl oxazolidinones

In an effort to discover potent antibacterials based on the entropically favored 'bioactive conformation' approach, a series of novel tricyclic molecules mimicking the conformationally constrained structure of Linezolid is reported. Based on the initial tricyclic molecule 1, the benzazepine derivative 2 was designed where the tricyclic structure had more flexibility around C-N bond compared to 1. While, the molecule 2 was less active, the molecule 3 showed promising antibacterial activity presumably after having obtained rigidity due to pyrrole ring. The syntheses, SAR studies, and evaluation of 3 as a lead compound are reported.