Unique Properties of Eukaryote-Type Actin and Profilin Horizontally Transferred to Cyanobacteria

A eukaryote-type actin and its binding protein profilin encoded on a genomic island in the cyanobacterium Microcystis aeruginosa PCC 7806 co-localize to form a hollow, spherical enclosure occupying a considerable intracellular space as shown by in vivo fluorescence microscopy. Biochemical and biophysical characterization reveals key differences between these proteins and their eukaryotic homologs. Small-angle X-ray scattering shows that the actin assembles into elongated, filamentous polymers which can be visualized microscopically with fluorescent phalloidin. Whereas rabbit actin forms thin cylindrical filaments about 100 µm in length, cyanobacterial actin polymers resemble a ribbon, arrest polymerization at 5-10 µm and tend to form irregular multi-strand assemblies. While eukaryotic profilin is a specific actin monomer binding protein, cyanobacterial profilin shows the unprecedented property of decorating actin filaments. Electron micrographs show that cyanobacterial profilin stimulates actin filament bundling and stabilizes their lateral alignment into heteropolymeric sheets from which the observed hollow enclosure may be formed. We hypothesize that adaptation to the confined space of a bacterial cell devoid of binding proteins usually regulating actin polymerization in eukaryotes has driven the co-evolution of cyanobacterial actin and profilin, giving rise to an intracellular entity

#DasMag: het literaire tijdschrift als community

In this article we discuss the Dutch literary magazine Das Magazin (2011-present) in the light of three hypotheses about the functioning of literary magazines as communities in present-day culture: the makers refuse to be part of the linear narrative of conventional modern literary history by not positioning themselves against their predecessors’ poetics or literary practice; the authorship that is practiced and represented in the community is a symptom of the current emancipation of the heteronomous writer, and: within the community there is no disdain for the fan culture of readers without self-evident knowledge of the conventions of the autonomous literary field

Requirements certification for offshoring using LSPCM

Requirements hand-over is a common practice in software development off shoring. Cultural and geographical distance between the outsourcer and supplier, and the differences in development practices hinder the communication and lead to the misinterpretation of the original set of requirements. In this article we advocate requirements quality certification using LSPCM as a prerequisite for requirements hand-over. LSPCM stands for LaQuSo Software Product Certification Model that can be applied by non-experienced IT assessors to verify software artifacts in order to contribute to the successfulness of the project. To support our claim we have analyzed requirements of three off shoring projects using LSPCM. Application of LSPCM revealed severe flaws in one of the projects. The responsible project leader confirmed later that the development significantly exceeded time and budget. In the other project no major flaws were detected by LSPCM and it was confirmed that the implementation was delivered within time and budget. Application of LSPCM to the projects above also allowed us to refine the model for requirements hand-over in software development off shoring

Protein refolding is required for assembly of the type three secretion needle

Pathogenic Gram-negative bacteria use a type three secretion system (TTSS) to deliver virulence factors into host cells. Although the order in which proteins incorporate into the growing TTSS is well described, the underlying assembly mechanisms are still unclear. Here we show that the TTSS needle protomer refolds spontaneously to extend the needle from the distal end. We developed a functional mutant of the needle protomer from Shigella flexneri and Salmonella typhimurium to study its assembly in vitro. We show that the protomer partially refolds from α-helix into β-strand conformation to form the TTSS needle. Reconstitution experiments show that needle growth does not require ATP. Thus, like the structurally related flagellar systems, the needle elongates by subunit polymerization at the distal end but requires protomer refolding. Our studies provide a starting point to understand the molecular assembly mechanisms and the structure of the TTSS at atomic level