A regulatory element within a gene of a ribosomal protein operon of Escherichia coli negatively controls expression by decreasing the translational efficiency

Summary The trmD operon of Escherichia coli consists of the genes for the ribosomal protein (r-protein) S16, a 21 kDa protein (21K) of unknown function, the tRNA(m¹G37)methyltransferase (TrmD), and r-protein L19, in this order. Previously we have shown that the steady-state amount of the two r-proteins exceeds that of the 21K and TrmD proteins 12- and 40-fold, respectively, and that this differential expression is solely explained by translational regulation. Here we have constructed translational gene fusions of the trmD operon and lacZ. The expression of a lacZ fusion containing the first 18 codons of the 21K protein gene is 15-fold higher than the expression of fusions containing 49 or 72 codons of the gene. This suggests that sequences between the 18th and the 49th codon may act as a negative element controlling the expression of the 21K protein gene. Evidence is presented which demonstrates that this regulation is achieved by reducing the efficiency of translation.     

Evolution of the amino acid substitution in the mammalian myoglobin gene

Summary Multivariate statistical analyses were applied to 16 physical and chemical properties of amino acids. Four of these properties; volume, polarity, isoelectric point (charge), and hydrophobicity were found to explain adequately 96% of the total variance of amino acid attributes. Using these four quantitative measures of amino acid properties, a structural discriminate function in the form of a weighted difference sum of squares equation was developed. The discriminate function is weighted by the location of each particular residue within a given tertiary structure and yields a numerical discriminate or difference value for the replacement of these residues by different amino acids. This resulting discriminate value represents an expression of the perturbation in the local positional environment of a protein when an amino acid substitution occurs. With the use of this structural discriminate function, a residue by residue comparison of the known mammalian myoglobin sequences was carried out in an attempt to elucidate the positions of possible deviations from the known tertiary structure of sperm whale myoglobin. Only 11 of the 153 residue positions in myoglobin demonstrated possible structural deviations. From this analysis, indices of difference were calculated for all amino acid exchanges between the various myoglobins. All comparisons yielded indices of difference that were considerably lower than would be expected if mutations had been fixed at random, even if the organization of the genetic code is taken into consideration. On the basis of these results, it is inferred that some form of selection has acted in the evolution of mammalian myoglobins to favor amino acid substitutions that are compatible with the retention of the original conformation of the protein.     

Functional and structural analysis of acetylcholine receptor-rich membranes after negative staining

Phosphotungstate (pH 7.4) used for negative staining of membranes from Torpedo electric tissue rich in acetylcholine receptor does not affect binding properties and cation permeability of the receptor and its ion channel. Uranyl salts, frequently used for negative staining, precipitate the receptor-rich membranes making measurements of ligand binding and ion-permeability regulation impossible. The gross ultrastructure in the two stains is not significantly different, but for future high-resolution electron microscopy aiming at visualizing structural details of functional receptor molecules it is necessary to resort to a stain preserving native and active receptor. Uranyl salts are not applicable for this purpose. The electron micrographs obtained with phosphotungstate reveal two distinct structures in the receptor-rich membrane: a closed ring ('doughnut') and an open ring ('horseshoe'), with a ratio of abundance of about 3:2.     

Effect of Potassium on the Release of [3H]Noradrenaline from Rabbit and Human Pulmonary Artery

The release of [3H]noradrenaline ( [3H]NA) from rabbit and human isolated pulmonary artery has been measured. Removal of external potassium ions enhanced both the resting and stimulated release of [3H]NA from the strips. On adding K+ to tissues which had been suspended in K+-free Krebs solution, the release of [3H]NA was reduced in both stimulated and unstimulated tissues. Selective inhibition of presynaptic alpha 2-adrenoceptors by yohimbine significantly potentiated the release of [3H]NA evoked by stimulation in K+-free solution. The presynaptic inhibitory effect of NA was much less pronounced when the release was enhanced by the removal of external K+. Since the activity of NA, K-ATPase may be affected by removing K+ or by adding it to tissue previously kept in K+-free solution, the results may indicate involvement of the sodium pump in NA release.     

Caenorhabditis briggsae: aging and the structural turnover of the outer cuticle surface and the intestine.

The exposed surface of Caenorhabditis briggsae was examined for the presence of neuraminic acid, hyaluronic acid, and glucuronic acid. None of these molecules was detected. In young nematodes the presence of a surface coat was demonstrated. This surface coat appeared to shrink with age. Ruthenium red staining suggested the presence of acid mucopoly-saccharides on the outer surface. Feeding the nematodes on cationized ferritin enabled visualization of a matrix surrounding the intestinal brush border. Experiments with an inhibitor of acid mucopolysaccharide synthesis suggested that there is no turnover of acid mucopolysaccharides after the final molt of C. briggsae.