The structure and function of Escherichia coli penicillin-binding protein 3

Escherichia coli penicillin-binding protein PBP3 is a key element in cell septation. It is presumed to catalyse a transpeptidation reaction during biosynthesis of the septum peptidoglycan but, in vitro, its enzymatic activity has only been demonstrated with thiolester analogues of the natural peptide substrate. It has no detectable transglycosylase activity with lipid II as substrate. This tripartite protein is constructed of an N-terminal membrane anchor-containing module that is essential for cell septation, a non-penicillin-binding (n-PB) module of unknown function and a C-terminal penicillin-binding (PB) module exhibiting all the characteristic motifs of penicilloyl serine transferases. The n-PB module, which is required for the folding and stability of the PB module, may provide recognition sites for other cell division proteins. Initiation of septum formation is not PBP3-dependent but rests on the appearance of the FtsZ ring, and is thus penicillin-insensitive. The control of PBP3 activity during the cell cycle is briefly discussed.     

On the decrement function of an action potential in a volume conductor

Zusammenfassung Eine Modifikation der Feldgleichung vonLorente de Nó wird einer Fourier-Transformation unterworfen. Dabei zeigt sich, dass das Dekrement einer jeden Frequenz eineK ₀-Funktion in ihrem eigenen Maßstab darstellt. Die theoretische Dekrementkurve stimmt gut mit der experimentell ausgearbeiteten überein.     

nDsbD: a redox interaction hub in the Escherichia coli periplasm

DsbD is a redox-active protein of the inner Escherichia coli membrane possessing an N-terminal (nDsbD) and a C-terminal (cDsbD) periplasmic domain. nDsbD interacts with four different redox proteins involved in the periplasmic disulfide isomerization and in the cytochrome c maturation systems. We review here the studies that led to the structural characterization of all soluble DsbD domains involved and, most importantly, of trapped disulfide intermediate complexes of nDsbD with three of its four redox partners. These results revealed the structural features enabling nDsbD, a ‘redox hub’ with an immunoglobulin-like fold, to interact efficiently with its different thioredoxin-like partners. Received 3 February 2006; received after revision 1 March 2006; accepted 5 April 2006     

A chromosome mutation affecting the number of nucleoli inXenopus borealis Parker

Résumé L'examen cytologique de la descendance de 2Xenopus borealis révéla 50% d'individus dotés de noyaux à 1 et 2 nucléoles (situation normale) et 50% à 1, 2 et 3 nucléoles. Le caryotype de ces derniers démontra la présence de 3 organisateurs nucléolaires, au lieu de 2, l'origine de l'élément supplémentaire relevant d'une translocation réciproque entre 4 et 7.

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Supported by a grant (No. 3.60.68) from the Fonds national suisse de la Recherche Scientifique and the George and Antoine Claraz donation.

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Unpublished research in this laboratory has shown thatXenopus laevis borealis (Parker) is a species on its own right and we propose to name itXenopus borealis (Parker).

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Material collected byFischberg andKobel, who express their gratitude to the Fisheries and Game Dept. of Kenya for permission to collect frogs of the genusXenopus.

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Acknowledgments. The authors wish to thank Mrs.J. Tymowska and MissE. Ackermann for their technical advice; they are grateful to Mr.J. Jackson, MissM. C. Payot, MissL. Ricard and Mr.P. Grutter for their assistance and useful help.