Antipseudomonal activity enhancement of luminescent iridium(iii) dipyridylamine complexes under visible blue light.

Cyclometallated iridium(iii) dipyridylamine complexes present antibacterial activity against P. aeruginosa, a highly resistant pathogenic bacterium. This activity is increased when the complex is conjugated to biotin, a bacterial nutrient, and a MIC of 4 µM (4 µg mL-1) has been observed. The irradiation of P. aeruginosa cultures with blue LED light potentiates the anti-bacterial activities of these iridium(iii) complexes when they are conjugated to a glycoside.

[A glimpse on Staphylococcus aureus translation machinery and its control].

Staphylococcus aureus is a major opportunistic and versatile pathogen. Because the bacteria rapidly evolve multi-resistances towards antibiotics, there is an urgent need to find novel targets and alternative strategies to cure bacterial infections. Here, we provide a brief overview on the knowledge acquired on S. aureus ribosomes, which is one of the major antibiotic targets. We will show that subtle differences exist between the translation at the initiation step of Gram-negative and Gram-positive bacteria although their ribosomes display a remarkable degree of resemblance. In addition, we will illustrate using specific examples the diversity of mechanisms controlling translation initiation in S. aureus that contribute to shape the expression of the virulence factors in a temporal and dynamic manner.

Regulatory RNAs as mediators of virulence gene expression in bacteria.

Bacteria exploit functional diversity of RNAs in a wide range of regulatory mechanisms to control gene expression. In last few years, small RNA molecules have been discovered at a staggering rate in bacteria, mainly in Escherichia coli. While functions of many of these RNA molecules are still not known, several of them behave as key effectors of adaptive responses, such as environmental cue recognition, stress response, and virulence control. Most fascinating, perhaps, is the discovery that mRNAs behave as direct sensors of small molecules or of environmental cues. The astonishing diversity of RNA-dependent regulatory mechanisms is linked to the dynamic properties and versatility of the RNA structure. In this review, we relate several recent studies in different bacterial pathogens that illustrate the diverse roles of RNA to control virulence gene expression.

Novel features in the tRNA-like world of plant viral RNAs.

tRNA-like domains are found at the 3' end of genomic RNAs of several genera of plant viral RNAs. Three groups of tRNA mimics have been characterized on the basis of their aminoacylation identity (valine, histidine and tyrosine) for aminoacyl-tRNA synthetases. Folding of these domains deviates from the canonical tRNA cloverleaf. The closest sequence similarities with tRNA are those found in valine accepting structures from tymoviruses (e.g. TYMV). All the viral tRNA mimics present a pseudoknotted amino acid accepting stem, which confers special structural and functional characteristics. In this review emphasis is given to newly discovered tRNA-like structures (e.g. in furoviruses) and to recent advances in the understanding of their three-dimensional architecture, which mimics L-shaped tRNA. Identity determinants in tRNA-like domains for aminoacylation are described, and evidence for their functional expression, as in tRNAs, is given. Properties of engineered tRNA-like domains are discussed, and other functional mimicries with tRNA are described (e.g. interaction with elongation factors and tRNA maturation enzymes). A final section reviews the biological role of the tRNA-like domains in amplification of viral genomes. In this process, in which the mechanisms can vary in specificity and efficiency according to the viral genus, function can be dependent on the aminoacylation properties of the tRNA-like domains and/or on structural properties within or outside these domains.

Specific tyrosylation of the bulky tRNA-like structure of brome mosaic virus RNA relies solely on identity nucleotides present in its amino acid-accepting domain.

Residues specifying aminoacylation by yeast tyrosyl-tRNA synthetase (TyrRS) of the tRNA-like structure present at the 3'-end of brome mosaic virus (BMV) RNA were determined by the in vitro approach using phage T7 transcripts. They correspond to nucleotides equivalent to base-pair C1-G72 and discriminator base A73 in the amino acid-acceptor branch of the molecule. No functional equivalents of the tyrosine anticodon residues, shown to be weakly involved in tyrosine identity of canonical tRNA(Tyr), were found in the BMV tRNA-like structure. This indicates a behaviour of this large and intricate molecule reminiscent of that of a minihelix derived from an amino acid-acceptor branch. Furthermore, iodine footprinting experiments performed on a tyrosylable BMV RNA transcript of 196 nt complexed to yeast TyrRS indicate that the amino acid-acceptor branch of the viral RNA is protected against cleavages as well as a hairpin domain, which is possibly located perpendicularly to its accepting branch. This domain without the canonical anticodon loop or the tyrosine anticodon acts as an anchor for TyrRS interaction leading to a better efficiency of tyrosylation.

Major tyrosine identity determinants in Methanococcus jannaschii and Saccharomyces cerevisiae tRNA(Tyr) are conserved but expressed differently.

Using in vitro tRNA transcripts and minihelices it was shown that the tyrosine identity for tRNA charging by tyrosyl-tRNA synthetase (TyrRS) from the archaeon Methanococcus jannaschii is determined by six nucleotides: the discriminator base A73 and the first base-pair C1-G72 in the acceptor stem together with the anticodon triplet. The anticodon residues however, participate only weakly in identity determination, especially residues 35 and 36. The completeness of the aforementioned identity set was verified by its tranfer into several tRNAs which then become as efficiently tyrosylatable as the wild-type transcript from M. jannaschii. Temperature dependence experiments on both the structure and the tyrosylation properties of M. jannaschii and yeast tRNA(Tyr) transcripts show that the archaeal transcript has greater structural stability and enhanced aminoacylation behaviour than the yeast transcript. Tyrosine identity in M. jannaschii is compared to that in yeast, and the conservation of the major determinant in both organisms, namely the C1-G72 pair, gives additional support to the existence of a functional connection between archaeal and eukaryotic aminoacylation systems.

Identity of tRNA for yeast tyrosyl-tRNA synthetase: tyrosylation is more sensitive to identity nucleotides than to structural features.

The specific aminoacylation of tRNA by yeast tyrosyl-tRNA synthetase does not rely on the presence of modified residues in tRNA(Tyr), although such residues stabilize its structure. Thus, the major tyrosine identity determinants were searched by the in vitro approach using unmodified transcripts produced by T7 RNA polymerase. On the basis of the tyrosylation efficiency of tRNA variants, the strongest determinants are base pair C1-G72 and discriminator residue A73 (the 5'-phosphoryl group on C1, however, is unimportant for tyrosylation). The three anticodon bases G34, U35, and A36 contribute also to the tyrosine identity, but to a lesser extent, with G34 having the most pronounced effect. Mutation of the GUA tyrosine anticodon into a CAU methionine anticodon, however, leads to a loss of tyrosylation efficiency similar to that obtained after mutation of the C1-G72 or A73 determinants. Transplantation of the six determinants into four different tRNA frameworks and activity assays on heterologous Escherichia coli and Methanococcus jannaschii tRNA(Tyr) confirmed the completeness of the tyrosine set and the eukaryotic character of the C1-G72 base pair. On the other hand, it was found that tyrosine identity in yeast does not rely on fine architectural features of the tRNA, in particular the size and sequence of the D-loop. Noticeable, yeast TyrRS efficiently charges a variant of E. coli tRNA(Tyr) with a large extra-region provided its G1-C72 base pair is changed to a C1-G72 base pair. Finally, tyrosylation activity is compatible with a +1 shift of the anticodon in the 3'-direction but is strongly inhibited if this shift occurs in the opposite 5'-direction.

Ribozyme processed tRNA transcripts with unfriendly internal promoter for T7 RNA polymerase: production and activity.

A limitation for a universal use of T7 RNA polymerase for in vitro tRNA transcription lies in the nature of the often unfavorable 5'-terminal sequence of the gene to be transcribed. To overcome this drawback, a hammerhead ribozyme sequence was introduced between a strong T7 RNA polymerase promoter and the tDNA sequence. Transcription of this construct gives rise to a 'transzyme' molecule, the autocatalytic activity of which liberates a 5'-OH tRNA transcript starting with the proper nucleotide. The method was optimized for transcription of yeast tRNA(Tgammar), starting with 5'-C1, and operates as well for yeast tRNA(Asp) with 5'-U1. Although the tRNAs produced by the transzyme method are not phosphorylated, they are fully active in aminoacylation with k(cat) and Km parameters quasi identical to those of their phosphorylated counterparts.

[Advantage of ECG self-recording by the patient]. / Was bringt die patienteneigene EKG-Registrierung?

The study reported here concerns new, computerized ECG devices (R-Test 160, Heartner) which the patient can carry in his pocket and use to register cardiac episodes. Seventy-two patients experiencing sudden episodes--not of daily occurrence--marked by palpitations or irregular pulse were supplied with a device on a total of 83 occasions. The total number of attacks registered was 93. The Heartner device was used by pressing it lightly over the precordial region. The R-Test instrument, on the other hand, required attachment of two conducting arm-bands. Forty-four (61%) of the patients had no organic heart disease. During a mean observation time of 17 +/- 9 days, 28 of the patients (39%) recorded symptomatic episodes, of which 11 consisted of normocardiac sinus rhythm, 7 of sinus tachycardia and only 10 (14%) of arrhythmia. The commonest reasons for a negative test result were freedom from episodes during the observation period (22 patients) and episodes of too short a duration (6 patients). In practice, arrhythmias are not easy to detect with these "home micro-Holters". Those registered correlate poorly with the subjective symptoms, an observation already reported in a number of other Holter studies. Moreover, immediate recording of any arrhythmia occurring is not possible with the devices used in our study. The average delay in starting a recording, caused by the need to attach and switch on the device, is one minute. These ECG devices are of practical use mainly for verifying functional cardiac disorders or as an alternative method in cooperative patients with arrhythmia episodes occurring infrequently and lasting at least one minute.

[Changes in the sinus beat following extrasystole as evidenced by the Holter ECG]. / Veränderungen des postextrasystolischen Sinusschlags im Holter-EKG.

In order to establish the nature and extent of alterations of a sinus beat following a ventricular extrasystole (VES), all two-channel Holter ECGs from 1984-86 were analyzed retrospectively. All passages suspicious for T wave alterations in the miniaturized ECG were written with 25 mm/sec paper speed and the sinus beats before and after a VES were compared (without interposed VES and ventricular tachycardia). In 57 men and 43 women, 100 ECGs were found with monomorphic (25%) or polymorphic (75%) VES. On the basis of clinical, noninvasive diagnostic procedures, 65 patients had cardiovascular disease. In 42 patients from all those investigated, alterations of the T wave of the postextrasystolic sinus beat were seen. These took the form of flattening in 62%, a rise in 26% and inversion of the T wave in 12% (chiefly on channel 2). While the ST segment and the U wave were always unaltered, a shortening of PQ was observed in 40%. These alterations in the T wave and the PQ time do not allow a distinction between persons with and without cardiovascular disease.

[Ergometrically determined work capacity in chronic hemodialysis treatment]. / Ergometrisch bestimmte Arbeitskapazität bei chronischer Hämodialysebehandlung.

To evaluate the degree of physical activity in hemodialysis patients, working capacity was assessed by bicycle ergometry in 16 hemodialysis patients (mean age 47 +/- 12 [SD] years). The mean length of dialysis treatment was 21 +/- 17 months. The laboratory and clinical findings were as follows (mean values +/- SD): urea 34 +/- 6 mmol/l; creatinine 1127 +/- 169 mumol/l; potassium 5.7 +/- 0.63 mmol/l; calcium 2.25 +/- 0.22 mmol/l; phosphate 1.76 +/- 0.54 mmol/l; hemoglobin 8.54 +/- 1.02 g/dl; hematocrit 26.1 +/- 2.9%; blood pressure 140 +/- 18/86 +/- 9 mm Hg; nerve conduction velocity 39.5 +/- 6.5 m/sec. Mean working capacity was 58 +/- 31 W (41 +/- 24% of normal values) and the specific working capacity (watts/kg body weight) was 0.79 +/- 0.54. The duration of exercise testing was 4.9 +/- 2 min. The ergometry had to be discontinued because of the following reasons: leg fatigue (10 patients); general fatigue (3); dyspnea (1); attainment of maximal heart rate (2). The maximal blood pressure during exercise testing was 149 +/- 21/86 +/- 14 mm Hg and the maximal increase in heart rate 117 +/- 34 beats/min. In patients treated with a beta-blocker agent for hypertension, maximal increase in blood pressure was comparable to normotensive patients. There was a negative correlation between working capacity and the age of the patients (r = 0.77; p less than 0.01). A positive correlation was found between working capacity and the serum creatinine level (r = 0.52; p less than 0.05).

The antiarrhythmic effects of controlled release disopyramide phosphate and long acting propranolol in patients with ventricular arrhythmias.

The antiarrhythmic effect of slow-release disopyramide phosphate (DR) 300 mg twice daily and of long-acting propranolol (PR) 1 X 160 mg daily was compared in a randomized cross-over study in patients with premature ventricular beats (PVB). 12 patients with PVB (Lown Classes II-V) were given: placebo I for 3 days, DR or PR for 7 days, placebo II for 5 days and PR or DR for 7 days. During each study phase Holter-ECG recordings were taken over a period of 24 h. With DR 6 patients showed a positive qualitative effect, improving by at least one Lown class, whereas only 2 patients did so with PR. With DR reduction of PVB greater than 80% occurred in 7 patients, and with PR in 2 patients. In all patients with any reduction in PVB, the median decrease was 85% with DR and 59% with PR. The overall results suggest that the antiarrhythmic effect of disopyramide phosphate in the slow-release preparation is at least satisfactory and comparable to that of disopyramide phosphate in the standard capsule formulation given in the usual and more complicated regime of four divided doses. The antiarrhythmic effect of PR in the recommended dose as given was not convincing.

[Antiarrhythmic effect of disopyramid retard versus propranolol retard in ventricular extrasystole]. / Die antiarrhythmische Wirkung von Disopyramid Retard versus Propranolol Retard bei ventrikulärer Extrasystolie.

The antiarrhythmic effect of disopyramide retard (DR) in a dose of 2 X 300 mg/day, propranolol retard (PR) in one of 1 X 160 mg/day and placebo was compared in a randomized crossover study in patients with ventricular premature beats (VPB). 10 patients with VPB (Lown classes II-V) were given the drugs as follows: placebo I for 3 days. DR or PR for 7 days, placebo II for 5 days and PR or DR for 7 days. During every phase Holter ECG was registered over a period of 24 hours. Under DR 6 patients showed a favourable qualitative effect improving by at least one Lown class, while under PR only one patient did so. Under DR an over 80% reduction of VPB occurred in 6 patients and under PR in one patient. In all patients with any reduction of VPB this reduction was 79% under DR and 57% under PR. These results suggest that the antiarrhythmic effect of disopyramide in slow release preparations is comparable with that of disopyramide in standard capsule formulation given in the usual and more complicated regime with four divided doses. In the above mentioned (and still recommended) dose PR has no antiarrhythmic effect.