C-terminal processing of yeast Spt7 occurs in the absence of functional SAGA complex

Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.     

The impulsive response of sandwich beams: Analytical and numerical investigation of regimes of behaviour

An analytical model is developed to classify the impulsive response of sandwich beams based on the relative time-scales of core compression and the bending/stretching response of the sandwich beam. It is shown that an overlap in time scales leads to a coupled response and to the possibility of an enhanced shock resistance. Four regimes of behaviour are defined: decoupled responses with the sandwich core densifying partially or completely, and coupled responses with partial or full core densification. These regimes are marked on maps with axes chosen from the sandwich beam transverse core strength, the sandwich beam aspect ratio and the level of blast impulse. In addition to predicting the time-scales involved in the response of the sandwich beam, the analytical model is used to estimate the back face deflection, the degree of core compression and the magnitude of the support reactions. The predictions of the analytical model are compared with finite element (FE) simulations of impulsively loaded sandwich beams comprising an anisotropic foam core and elastic, ideally plastic face-sheets. The analytical and numerical predictions are in good agreement up to the end of core compression. However, the analytical model under-predicts the peak back face deflection and over-predicts the support reactions, especially for sandwich beams with high strength cores. The FE calculations are employed to construct design charts to select the optimum transverse core strength that either minimises the back face deflections or support reactions for a given sandwich beam aspect ratio or blast impulse. Typically, the value of the transverse core strength that minimises the back face deflection also minimises the support reactions. However, the optimal core strength depends on the level of blast impulse, with higher strength cores required for greater blasts.     

Examining thermal stability and structure property relationships in coatings based on linear aromatic poly(methoxy-thiocyanurate)s

A series of copoly(methoxy-thiocyanurate)s is prepared in good yield and purity, and fully characterised. Many of the resulting polymers, formed at room temperature using phase transfer catalysis, can be cast into films with good resilience and thermal stability (some examples suffer practically no mass loss when held isothermally at 190 °C and only display appreciable losses when held continuously at 225 °C). Char yields of 61–64% are achieved in nitrogen depending on backbone structure. Some problems were encountered with solubility, particularly with copolymers, which limited molecular weights analysis, but values of M_n = 7000–10,000 g mol⁻¹ were obtained for the polycyanurate and polythiocyanurate homopolymers. DSC reveals polymerisation exotherms with maxima at 197–207 °C (ΔH_p = 39–48 kJ/mol), which are believed to be due to isomerisation of the (activation energies span 172–205 kJ/mol), since X-ray powder diffraction measurements reveal no evidence of crystalline structure in the resulting product.     

Prediction of polymerization shrinkage using molecular modeling

Group interaction modeling (GIM) is used to predict the changes in the volume and, therefore, shrinkage of a wide variety of commonly encountered acrylate and methacrylate monomers during polymerization. The predictions of the model are in excellent agreement with experimental data available in the literature. It is demonstrated that, given appropriate estimations of the ultimate matrix morphology, GIM can be used to give estimates of polymerization shrinkage in three‐dimensional crosslinked polymer networks that relate well to experimental data available for dental composite matrices. GIM provides a very useful framework within which the phenomenon of polymerization shrinkage can be considered. The approach challenges certain common misconceptions relating conversion to shrinkage. The limitations of this approach are discussed, and targets for future research are clearly outlined that could extend the scope of this methodology to encompass novel systems for which morphological information is not available. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 528–548, 2003     

A 2,3-butanedione protected chiral glycine equivalent--a new building block for the stereoselective synthesis of enantiopure N-protected alpha-amino acids

A new chiral glycine equivalent 7 has been synthesised from glycidol using a chiral memory protocol, and its use in the synthesis of N-Z protected alpha-amino acids was demonstrated in a series of diasteroselective lithium enolate alkylation reactions and subsequent acid hydrolyses.