Copolymerization of Styrene and Methyl Methacrylate in Ternary Oil-in-Water Microemulsions: Comments on a Paper by Gan et al

Exptl. data presented by L.M. Gan et al. are reinterpreted with the use of the error-in-variables method. The recalcd. reactivity ratios in microemulsion hardly deviate from earlier reported bulk copolymn. values. Furthermore it is shown that monomer sequence distribution as a function of copolymer compn. is equally well described by bulk reactivity ratios as it is by microemulsion reactivity ratios. This can easily be explained from the fact that the relation between monomer sequence distribution and copolymer compn. is governed by the reactivity ratio product, rather than by the sep. reactivity ratios. It is found that the reactivity ratio product in microemulsion does not significantly deviate from that in bul

The contributions of Prof. Kenneth F. O'Driscoll to radical copolymerization kinetics

Among the many contributions that Kenneth ‘Ken’ O'Driscoll made to advance the understanding of radical polymerization kinetics was the implementation of proper statistical procedures for extracting (monomer) reactivity ratios from experimental data for copolymer composition. He emphasized the importance of experimental design, using non-linear regression, and a proper error analysis to construct reliable joint confidence intervals. He disseminated his views on this topic in many conferences, including the influential Santa Margherita Ligure series which he initiated, and which helped kickstart the renaissance of radical polymerization kinetics. This brief retrospective honours both Ken's scientific contributions and his humanity

Imaging and imagination: understanding the endo-lysosomal system

Lysosomes are specialized compartments for the degradation of endocytosed and intracellular material and essential regulators of cellular homeostasis. The importance of lysosomes is illustrated by the rapidly growing number of human disorders related to a defect in lysosomal functioning. Here, we review current insights in the mechanisms of lysosome biogenesis and protein sorting within the endo-lysosomal system. We present increasing evidence for the existence of parallel pathways for the delivery of newly synthesized lysosomal proteins directly from the trans-Golgi network (TGN) to the endo-lysosomal system. These pathways are either dependent or independent of mannose 6-phosphate receptors and likely involve multiple exits for lysosomal proteins from the TGN. In addition, we discuss the different endosomal intermediates and subdomains that are involved in sorting of endocytosed cargo. Throughout our review, we highlight some examples in the literature showing how imaging, especially electron microscopy, has made major contributions to our understanding of the endo-lysosomal system today

The conserved dileucine- and tyrosine-based motifs in MLV and MPMV envelope glycoproteins are both important to regulate a common Env intracellular trafficking

BACKGROUND: Retrovirus particles emerge from the assembly of two structural protein components, Gag that is translated as a soluble protein in the cytoplasm of the host cells, and Env, a type I transmembrane protein. Because both components are translated in different intracellular compartments, elucidating the mechanisms of retrovirus assembly thus requires the study of their intracellular trafficking. RESULTS: We used a CD25 (Tac) chimera-based approach to study the trafficking of Moloney murine leukemia virus and Mason-Pfizer monkey virus Env proteins. We found that the cytoplasmic tails (CTs) of both Env conserved two major signals that control a complex intracellular trafficking. A dileucine-based motif controls the sorting of the chimeras from the trans-Golgi network (TGN) toward endosomal compartments. Env proteins then follow a retrograde transport to the TGN due to the action of a tyrosine-based motif. Mutation of either motif induces the mis-localization of the chimeric proteins and both motifs are found to mediate interactions of the viral CTs with clathrin adaptors. CONCLUSION: This data reveals the unexpected complexity of the intracellular trafficking of retrovirus Env proteins that cycle between the TGN and endosomes. Given that Gag proteins hijack endosomal host proteins, our work suggests that the endosomal pathway may be used by retroviruses to ensure proper encountering of viral structural Gag and Env proteins in cells, an essential step of virus assembly

Interaction of the Coronavirus Infectious Bronchitis Virus Membrane Protein with β-Actin and Its Implication in Virion Assembly and Budding

Coronavirus M protein is an essential component of virion and plays pivotal roles in virion assembly, budding and maturation. The M protein is integrated into the viral envelope with three transmembrane domains flanked by a short amino-terminal ectodomain and a large carboxy-terminal endodomain. In this study, we showed co-purification of the M protein from coronavirus infectious bronchitis virus (IBV) with actin. To understand the cellular factors that may be involved in virion assembly, budding and maturation processes, IBV M was used as the bait in a yeast two-hybrid screen, resulting in the identification of β-actin as a potentially interacting partner. This interaction was subsequently confirmed by coimmunoprecipitation and immunofluorescence microscopy in mammalian cells, and mutation of amino acids A159 and K160 on the M protein abolished the interaction. Introduction of the A159-K160 mutation into an infectious IBV clone system blocks the infectivity of the clone, although viral RNA replication and subgenomic mRNA transcription were actively detected. Disruption of actin filaments with cell-permeable agent cytochalasin D at early stages of the infection cycle led to the detection of viral protein synthesis in infected cells but not release of virus particles to the cultured media. However, the same treatment at late stages of the infection cycle did not affect the release of virus particles to the media, suggesting that disruption of the actin filaments might block virion assembly and budding, but not release of the virus particles. This study reveals an essential function of actin in the replication cycle of coronavirus