Regulation of Escherichia coli secA mRNA translation by a secretion-responsive element.

The Escherichia coli secA gene, whose translation is responsive to the proficiency of protein export within the cell, is the second gene in a three-gene operon and is flanked by gene X and mutT. By using gene fusion and oligonucleotide-directed mutagenesis techniques, we have localized this translationally regulated site to a region at the end of gene X and the beginning of secA. This region has been shown to bind SecA protein in vitro. These studies open the way for a direct investigation of the mechanism of secA regulation and its coupling to the protein secretion capability of the cell.     

Repression of lipopolysaccharide biosynthesis in Escherichia coli by an antisense RNA of Acetobacter methanolicus phage Acm1

Lysogenic Acetobacter methanolicus strains carrying the prophage Acm1 were found to be unable to synthesize both the capsutar polysaccharide (CPS) and the O-specific side-chain of lipopolysaccharide (LPS) and to represent rough variants of the host bacterium. A 262 bp DNA fragment of phage Acm1, obviously required for interference with LPS biosynthesis, was cloned and expressed in Escherichia coli Independently of the O-type, transformation of various E. coli strains with the recombinant DNA resulted in a suppression of biosynthesis of the O-specific chains. The DNA fragment of phage Acm1 contained three very short open reading frames of 21, 24, and 36 bp. However, attempts to express phage-encoded peptides were not successful. Instead, the Acm1-derived DNA fragment was shown to code for the synthesis of a trans-acting RNA molecule of 97 nucleotides, designated lbi (L PS b iosynthesis-i nterfering) RNA. This RNA contains sequence complementarity to E. coli target RNA sequences and appears to have the ability to form intracellularly RNA hybrid duplexes with mRNA. The data presented in this study support the hypothesis that the phenotypic effect of conversion to rough-type LPS is accompanied by the expression of an antisense RNA of phage Acm1.     

Learning-Induced Expression of Meningeal Ependymin mRNA and Demonstration of Ependymin in Neurons and Glial Cells

Abstract: The turnover of a CNS-specific cell adhesion glycoprotein, ependymin, has earlier been found to increase during periods of neuronal plasticity. Here, ependymin mRNA expression was analyzed by semiquantitative in situ hybridization in goldfish. Learning of an active avoidance response resulted in a significant increase in ependymin mRNA expression 20 min to 4 h after acquisition of the task. In contrast, yoked control animals that were exposed to the same numbers of conditioned and unconditioned stimuli in a random, unpaired manner exhibited a strong down-regulation of ependymin mRNA. Hybridization signals were also increased by injection of anti-ependymin antiserum into brain ventricles. Ependymin mRNA was exclusively localized to reticular-shaped fibroblasts of the inner endomeningeal cell layer. Immunoelectron microscopic investigation, however, revealed ependymin also in distinct neuronal and glial cell populations in which no ependymin mRNA had been detected. Uptake of meningeal protein factors into glial and neuronal cells may therefore be of functional importance for plastic adaptations of the CNS.     

ARDRA and RAPD-fingerprinting reject the sibling species concept for the ciliate Paramecium caudatum (Ciliophora, Protoctista)

Morphologically indistinguishable sibling species also known as syngens are a characteristic taxonomic feature of the ciliate genus Paramecium . This has been convincingly demonstrated for the P. aurelia species complex. For a long time this feature has also been assumed for P. caudatum . Classical morphology based techniques of taxonomic analysis are often inefficient to study sibling specie. We therefore investigated 14 P. caudatum strains of seven supposedly different syngens using random amplified polymorphic DNA (RAPD)-fingerprinting and amplified ribosomal DNA restriction analyses (ARDRA, Riboprinting). The RAPD patterns revealed by five different random primers were similar between the different strains of the same syngen (similarity index ranging from 73 to 91%) and also between strains of supposedly different syngens (similarity index ranging from 67 to 91%). The amplified 18S rRNA-fragments of supposedly different syngens, as well as the restriction patterns of these fragments digested by five different endonucleases, were identical for all investigated P. caudatum stains. Consequently we reject the sibling species hypothesis for P. caudatum . According to our molecular analysis, P. caudatum is not a species complex, but just one single species.     

Specificity of G protein beta and gamma subunit interactions.

Multiple heterotrimeric guanine nucleotide binding protein (G protein) subunits have evolved to couple a large variety of receptors to intracellular effectors. G protein beta gamma subunits are essential for efficient coupling of alpha subunits to receptors, and they are also important for modulation of effectors. Several different beta and gamma subunits exist, but it is not known whether all possible combinations of beta and gamma can form functional dimers. To answer this question, we have compared the ability of in vitro translated beta 1, beta 2, and beta 3 to form dimers with either gamma 1 or gamma 2. Dimerization was monitored by gel filtration, resistance to tryptic digestion, and chemical cross-linking. The results indicate that beta 1 binds both gamma subunits, beta 2 binds only gamma 2, and beta 3 will bind neither gamma 1 or gamma 2. Hence, the occurrence of beta gamma dimers may be partially regulated by the ability of the subunits to associate. Specificity of dimerization might allow cells to co-express multiple beta and gamma subunits while maintaining efficient and specific signal transduction.     

Adenosine/Adenine-Containing Nucleotides in the Leaves and Roots of Young Barley Plants after Infection of the Primary Leaf by Erysiphe graminis

The levels of adenosine, the adenine nucleotides AMP, ADP, ATP, as well as NAD, NADP, protein and chlorophyll were determined in young barley plants of which the primary leaves were infected by Erysiphe graminis DC. f. sp. hordei MARCHAL. The largest changes of these metabolite levels, compared to the non-infected control, occurred in the infected leaf and to a lesser degree also in the roots and in healthy younger leaves. The increase in the levels of most metabolites in the primary leaf revealed the sink property of this infected tissue and possible stress or defence reactions of the host, whereas the reductions in the roots showed the impaired supply of this natural sink organ due to the infection. Changes in the healthy leaves were most pronounced in the tertiary leaf and may reflect metabolic stimulation in that healthy organ. The changes of the adenosine pool, a precursor of the adenine nucleotides, were discussed in terms of translocation and its possible role as a precursor for fungal purine nucleotide synthesis.     

Artificial selection on ant female caste ratio uncovers a link between female‐biased sex ratios and infection by Wolbachia endosymbionts

Social insect sex and caste ratios are well‐studied targets of evolutionary conflicts, but the heritable factors affecting these traits remain unknown. To elucidate these factors, we carried out a short‐term artificial selection study on female caste ratio in the ant Monomorium pharaonis. Across three generations of bidirectional selection, we observed no response for caste ratio, but sex ratios rapidly became more female‐biased in the two replicate high selection lines and less female‐biased in the two replicate low selection lines. We hypothesized that this rapid divergence for sex ratio was caused by changes in the frequency of infection by the heritable bacterial endosymbiont Wolbachia, because the initial breeding stock varied for Wolbachia infection, and Wolbachia is known to cause female‐biased sex ratios in other insects. Consistent with this hypothesis, the proportions of Wolbachia‐infected colonies in the selection lines changed rapidly, mirroring the sex ratio changes. Moreover, the estimated effect of Wolbachia on sex ratio (~13% female bias) was similar in colonies before and during artificial selection, indicating that this Wolbachia effect is likely independent of the effects of artificial selection on other heritable factors. Our study provides evidence for the first case of endosymbiont sex ratio manipulation in a social insect.     

The cytomegalovirus enhancer: a pan-active control element in transgenic mice.

In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney.