Functional analysis of the post-transcriptional regulator RsmA reveals a novel RNA-binding site.

The RsmA family of RNA-binding proteins are global post-transcriptional regulators that mediate extensive changes in gene expression in bacteria. They bind to, and affect the translation rate of target mRNAs, a function that is further modulated by one or more, small, untranslated competitive regulatory RNAs. To gain new insights into the nature of this protein/RNA interaction, we used X-ray crystallography to solve the structure of the Yersinia enterocolitica RsmA homologue. RsmA consists of a dimeric beta barrel from which two alpha helices are projected. From structure-based alignments of the RsmA protein family from diverse bacteria, we identified key amino acid residues likely to be involved in RNA-binding. Site-specific mutagenesis revealed that arginine at position 44, located at the N terminus of the alpha helix is essential for biological activity in vivo and RNA-binding in vitro. Mutation of this site affects swarming motility, exoenzyme and secondary metabolite production in the human pathogen Pseudomonas aeruginosa, carbon metabolism in Escherichia coli, and hydrogen cyanide production in the plant beneficial strain Pseudomonas fluorescens CHA0. R44A mutants are also unable to interact with the small untranslated RNA, RsmZ. Thus, although possessing a motif similar to the KH domain of some eukaryotic RNA-binding proteins, RsmA differs substantially and incorporates a novel class of RNA-binding site.

Protein-binding site at the immunoglobulin mu membrane polyadenylylation signal: possible role in transcription termination.

mRNAs specifying immunoglobulin mu and delta heavy chains are encoded by a single large, complex transcription unit (mu + delta gene). The transcriptional activity of delta gene segments in terminally differentiated, IgM-secreting B lymphocytes is 10-20 times lower than in earlier B-lineage cells expressing delta mRNA. We find that transcription of the mu + delta gene in IgM-secreting murine myeloma cells terminates within a region of 500-1000 nucleotides immediately following the mu membrane (mu m) polyadenylylation site. Transcription decreases only minimally through this region in murine cell lines representative of earlier stages in B-cell development. A DNA fragment containing the mu m polyadenylylation signal gives protein-DNA complexes with different mobilities in gel retardation assays with nuclear extracts from myeloma cells than with nuclear extracts from earlier B-lineage cells. However, using a recently developed "footprinting" procedure in which protein-DNA complexes resolved in gel retardation assays are subjected to nucleolytic cleavage while still in the polyacrylamide gel, we find that the DNA sequences protected by factors from the two cell types are indistinguishable. The factor-binding site on the DNA is located 5' of the mu m polyadenylylation signal AATAAA and includes the 15-nucleotide-long A + T-rich palindrome CTGTAAACAAATGTC. This type of palindromic binding site exhibits orientation-dependent activity consistent with the reported properties of polymerase II termination signals. This binding site is followed by two sets of directly repeated DNA sequences with different helical conformation as revealed by their reactivity with the chemical nuclease 1,10-phenanthroline-copper. The close proximity of these features to the signals for mu m mRNA processing may reflect a linkage of the processes of developmentally regulated mu m polyadenylylation and transcription termination.

La "troisième quête" du Jésus de l'histoire

(Résumé de l'ouvrage) Que sait-on aujourd'hui de Jésus Christ ? De quel Christ parle-t-on? La confrontation entre théologiens et exégètes se révèle extraordinairement fructueuse et plus que jamais nécessaire.

Le conflit des interprétations en histoire. Lectures juives et chrétiennes de la chute de Jérusalem

(Résumé de l'ouvrage) Ce recueil regroupe les contributions de 35 spécialistes qui reprennent l'orientation principale ayant déterminé la recherche de Gottfried Hammann, professeur d'histoire du christianisme et de l'Eglise à la Faculté de théologie de l'Université de Neuchâtel. Les deux notions d'histoire et d'herméneutique indiquent les piliers sur lesquels repose l'arc historiographique contemporain, cette ligne courbe qui se dessine entre le passé et sa reconstitution. L'historien est appelé à réfléchir soigneusement à sa double tâche de documentaliste et d'interprète.

Le premier historien du christianisme

Le geste de Luc, personne ne le répétera après lui. On connaît, entre le Ier et le IIIe siècle, de nombreux auteurs d'évangile : plus de quatre, si l'on tient compte des évangiles apocryphes (Évangile selon Thomas, Évangile de Pierre, Évangile des Hébreux, etc.). On connaît également, toujours de la même période, plusieurs actes d'apôtre (Actes de Paul, Actes de Jean, Actes d'André). Mais personne, dans l'Antiquité, ne renouvellera le geste de Luc : écrire, à la suite de la biographie de Jésus, l'histoire de ses premiers disciples.