Karyophobic proteins : A category of abundant soluble proteins which accumulate in the cytoplasm

The cytoplasm of oocytes of Xenopus laevis is enriched in several soluble proteins which are either absent from the nucleus or are present there at very low concentrations. These molecules, collectively referred to as karyophobic (from the Greek verbs oβιν and oβλoθαi which are meant here in the sense of “to be afraid of” or “to avoid”) proteins represent more than 20% of the total soluble cytoplasmic proteins and include some of the most abundant soluble cellular components. They may be recovered from high-speed supernatant (S-100) fractions and, following sucrose gradient centrifugation, most of them appear in the form of complexes smaller than 8.5S. On denaturation in urea and two-dimensional gel electrophoresis these proteins appear to be comprised of polypeptides of widely different sizes (ca M_r 15 000–230 000) and isoelectric points covering a broad range of pH values (4.2–8.0). Gel filtration and isoelectric focusing of native karyophobic proteins show that the majority occur in acidic complexes smaller than M_r 150 000, including one case of a small karyophobic protein (C9; M_r 30 000). In contrast to karyophilic proteins and proteins equilibrating between nucleus and cytoplasm karyophobic soluble proteins from [³⁵S]methionine-labelled ooplasms, when injected into unlabelled oocytes, remain in the cytoplasm. Human proteins with a similar karyophobic behaviour have been identified in fractions of soluble proteins from HeLa cells; there, the major karyophobic protein (HCa, M_r 36 000) is also one of the most abundant soluble proteins.We conclude that the specific nucleocytoplasmic compartmentalization of soluble proteins is governed not only by the principles of exclusion of large molecules from nuclear uptake and the existence of karyophilic signals in certain proteins but that a series of soluble, globular proteins exist in the cytoplasm, which have other molecular features which selectively exclude them from distribution over the nucleus. The possible functional role of the selective enrichment of these abundant proteins, which so far have escaped attention, in establishing a cytoplasmic milieu is discussed.     

Survey of the Botrytis cinerea chitin synthase multigenic family through the analysis of six euascomycetes genomes.

We describe a strategy for systematic amplification of chitin synthase genes (chs) in the filamentous ascomycetes plant-pathogen Botrytis cinerea using PCR with multiple degenerate primers designed on specific and conserved sequence motifs. Eight distinct chs genes were isolated, named Bcchs I, II, IIIa, IIIb, IV, V, VI and VII. They probably constitute the entire chs multigenic family of this fungus, as revealed by careful analysis of six euascomycetes genomes. Bcchs I, IIIa, IIIb, IV and VI genes were subjected to DNA walking and their deduced amino acid sequences were compared by hydrophobic cluster analysis (HCA) to localize putative residues critical for CHS activity. HCA also enabled us to highlight three different transmembrane topologies of the CHS membranous isoenzymes. We found that the N-terminal region of the BcCHSI isoenzyme, and its orthologues in other euascomycetes, probably contain folded peptide motifs with conserved tyrosine residues. Their putative role is discussed. The BcCHSVII isoenzyme appeared to belong to a new class of CHS orthologues that was demonstrated by phylogenetic study to branch apart from division 1 and 2 of CHS.     

Walking over 4 Gya: Chemical Evolution from Photochemistry to Mineral and Organic Chemistries Leading to an RNA World

Here we overview the chemical evolution of RNA molecules from inorganic material through mineral-mediated RNA formation compatible with the plausible early Earth environments. Pathways from the gas-phase reaction to the formation of nucleotides, activation and oligomerization of nucleotides, seem to be compatible with specific environments. However, how these steps interacted is not clear since the chemical conditions are frequently different and can be incompatible between them; thus the products would have migrated from one place to another, suitable for further chemical evolution. In this review, we summarize certain points to scrutinize the RNA World hypothesis.     

Recontextualising Cellular Respiration in Upper Secondary Biology Education. Characteristics and Practicability of a Learning and Teaching Strategy

Since concepts may have different meanings in different contexts, students have to learn to recontextualise them, i.e. to adapt their meanings to a new context. It is unclear, however, what characteristics a learning and teaching strategy for recontextualising should have. The study aims to develop such a learning and teaching strategy for cellular respiration. The strategy consists of a storyline, consisting of three contexts, with embedded cognitive elements and some episodes focussed on recontextualising cellular respiration. Testing the strategy in two classes in upper secondary biology education showed that the strategy was largely practicable.     

TRAF4 Is a Novel Phosphoinositide-Binding Protein Modulating Tight Junctions and Favoring Cell Migration

Tumor necrosis factor (TNF) receptor-associated factor 4 (TRAF4) is frequently overexpressed in carcinomas, suggesting a specific role in cancer. Although TRAF4 protein is predominantly found at tight junctions (TJs) in normal mammary epithelial cells (MECs), it accumulates in the cytoplasm of malignant MECs. How TRAF4 is recruited and functions at TJs is unclear. Here we show that TRAF4 possesses a novel phosphoinositide (PIP)-binding domain crucial for its recruitment to TJs. Of interest, this property is shared by the other members of the TRAF protein family. Indeed, the TRAF domain of all TRAF proteins (TRAF1 to TRAF6) is a bona fide PIP-binding domain. Molecular and structural analyses revealed that the TRAF domain of TRAF4 exists as a trimer that binds up to three lipids using basic residues exposed at its surface. Cellular studies indicated that TRAF4 acts as a negative regulator of TJ and increases cell migration. These functions are dependent from its ability to interact with PIPs. Our results suggest that TRAF4 overexpression might contribute to breast cancer progression by destabilizing TJs and favoring cell migration.     

X chromosome inactivation in 30 girls with Rett syndrome: Analysis using the probe

Rett syndrome (RS) is a neurologic disorder with an exclusive incidence in females. A nonrandom X-inactivation could provide insight into the understanding of this disease. We performed molecular analysis based on the differential methylation of the active and inactive X with probe M27ß, taking into account the parental origin of the two Xs, in 30 control girls, 8 sisters, and 30 RS girls. In 27 control an 31 RS mothers, the inactivation status of the X transmitted to their daughters was also analyzed. The results showed a significantly increased frequency of partial paternal X inactivation (> 65%) in lymphocytes from 16/30 RS compared with 4/30 controls (P = 0.001). These results do not support the hypothesis of a monogenic X-linked mutation but should be taken into account when researching the etiology of this desease.