Optimum ground states for spin-32\frac{3}{2} chains

We present a set of {\em optimum ground states} for a large class of spin-$\frac{3}{2}$ chains. Such global ground states are simultaneously ground states of the local Hamiltonian, i.e. the nearest neighbour interaction in the present case. They are constructed in the form of a matrix product. We find three types of phases, namely a {\em weak antiferromagnet}, a {\em weak ferromagnet}, and a {\em dimerized antiferromagnet}. The main physical properties of these phases are calculated exactly by using a transfer matrix technique, in particular magnetization and two spin correlations. Depending on the model parameters, they show a surprisingly rich structure.Comment: LaTeX, 22 pages, 6 embedded Postscript figure

Depth of reading vocabulary in hearing and hearing-impaired children

The main point of our study was to examine the vocabulary knowledge of pupils in grades 3–6, and in particular the relative reading vocabulary disadvantage of hearing-impaired pupils. The achievements of 394 pupils with normal hearing and 106 pupils with a hearing impairment were examined on two vocabulary assessment tasks: a lexical decision task and a use decision task. The target words in both tasks represent the vocabulary children should have at the end of primary school. The results showed that most hearing pupils reached this norm, whereas most hearing-impaired pupils did not. In addition, results showed that hearing-impaired pupils not only knew fewer words, but that they also knew them less well. This lack of deeper knowledge remained even when matching hearing and hearing-impaired children on minimal word knowledge. Additionally, comparison of the two tasks demonstrated the efficacy of the lexical decision task as a measure of lexical semantic knowledge

Transport of Folded Proteins by the Tat System

The twin-arginine protein translocation (Tat) system has been characterized in bacteria, archaea and the chloroplast thylakoidal membrane. This system is distinct from other protein transport systems with respect to two key features. Firstly, it accepts cargo proteins with an N-terminal signal peptide that carries the canonical twin-arginine motif, which is essential for transport. Second, the Tat system only accepts and translocates fully folded cargo proteins across the respective membrane. Here, we review the core essential features of folded protein transport via the bacterial Tat system, using the three-component TatABC system of Escherichia coli and the two-component TatAC systems of Bacillus subtilis as the main examples. In particular, we address features of twin-arginine signal peptides, the essential Tat components and how they assemble into different complexes, mechanistic features and energetics of Tat-dependent protein translocation, cytoplasmic chaperoning of Tat cargo proteins, and the remarkable proofreading capabilities of the Tat system. In doing so, we present the current state of our understanding of Tat-dependent protein translocation across biological membranes, which may serve as a lead for future investigations

Structural organization of the twin-arginine translocation system in Streptomyces lividans.

&lt;p&gt;The twin-arginine translocation (Tat) system exports folded proteins across bacterial cytoplasmic membranes. Recently, genes encoding TatA, TatB and TatC homologues were identified in Streptomyces lividans and the functionality of the Tat pathway was demonstrated. Here, we have examined the localization and structural organization of the Tat components in S. lividans. Interestingly, besides being membrane-associated proteins, S. lividans TatA and TatB were also detected in the cytoplasm. TatC could only be detected in isolated membrane fractions. Whereas all TatC was found to be stably inserted in the membrane, part of membrane-associated TatA and TatB could be extracted following high salt, sodium carbonate or urea treatment suggesting a more loose association with the membrane. Finally, we have analyzed Tat complexes that could be purified from an S. lividans TatABC overproducing strain. From the cytoplasmic membrane, two types of high molecular mass Tat complexes could be isolated having a similar composition as those isolated from Escherichia coli. In the cytoplasm, TatA and TatB were detected as monomer or as homo-oligomeric complexes.&lt;/p&gt;</p

The twin-arginine translocation pathway is a major route of protein export in Streptomyces coelicolor

The twin-arginine translocation (Tat) pathway is a protein transport system for the export of folded proteins. Substrate proteins are targeted to the Tat translocase by N-terminal signal peptides harboring a distinctive R-R-x-Φ-Φ “twin-arginine” amino acid motif. Using a combination of proteomic techniques, the protein contents from the cell wall of the model Gram-positive bacterium Streptomyces coelicolor were identified and compared with that of mutant strains defective in Tat transport. The proteomic experiments pointed to 43 potentially Tat-dependent extracellular proteins. Of these, 25 were verified as bearing bona fide Tat-targeting signal peptides after independent screening with a facile, rapid, and sensitive reporter assay. The identified Tat substrates, among others, include polymer-degrading enzymes, phosphatases, and binding proteins as well as enzymes involved in secondary metabolism. Moreover, in addition to predicted extracellular substrates, putative lipoproteins were shown to be Tat-dependent. This work provides strong experimental evidence that the Tat system is used as a major general export pathway in Streptomyces