Characterization of a cross-linked DNA-Endonuclease VIII repair complex by electrospray ionization mass spectrometry

Electrospray mass spectrometry techniques were used to characterize components of the active site in Endonuclease VIII by identifying the amino acid sequence and the binding site for a tryptic peptide derived from Endo VIII in a cross-linked DNA-peptide complex. Endo VIII, a DNA repair enzyme with both glycosylase and lyase activities, was covalently bound to a thymidine glycol-containing oligodeoxynucleotide duplex by converting a transient Schiff base formed during the course of the glycosylase activity to a stable covalent bond by chemical reduction with sodium borohydride. After tryptic digestion of the initial product, the identification of the cross-linked peptide was deduced initially from the molecular mass of the tryptic product obtained by negative ion electrospray mass analysis. Nanospray tandem mass spectrometry (MS/MS) analysis of the tryptic product corroborated the molecular mass of the peptide fragment and verified the point of attachment to the oligomer, but failed to produce sufficient fragmentation to sequence the peptide completely. Direct evidence for the amino acid sequence of the peptide was obtained after enzymatic digestion of the DNA portion of the cross-linked DNA-peptide product and analysis by negative ion nanospray MS/MS. Examination of the ions from collision induced fragmentation disclosed that this substance was the N-terminal tryptic fragment of Endo VIII cross-linked to a portion of the oligomer, and that the N-terminal proline from Endo VIII was covalently bound to the residual deoxyribose moiety at the original location of the thymine glycol in the oligomer.     

Metallic stripe in two dimensions: stability and spin-charge separation

The problems of charge stripe formation, spin-charge separation, and stability of the antiphase domain wall (ADW) associated with a stripe are addressed using an analytical approach to the t- J(z) model. We show that a metallic stripe together with its ADW is the ground state of the problem in the low doping regime. The stripe is described as a system of spinons and magnetically confined holons strongly coupled to the two dimensional spin environment with holon-spin-polaron elementary excitations filling a one-dimensional band.     

Electrochemical and STM studies of 1-thio-β-D-glucose self-assembled on a Au(111) electrode surface

In this study, a Au(111) electrode is functionalized with a monolayer of 1-thio-β-D-glucose (β-Tg), producing a hydrophilic surface. A monolayer of β-Tg was formed on a Au(111) surface by either (1) potential-assisted deposition with the thiol in a supporting electrolyte or (2) passive incubation of a gold substrate in a thiol-containing solution. For each method, the properties of the β-Tg monolayer were investigated using cyclic voltammetry (CV), differential capacitance (DC), and chronocoulometry. In addition, electrochemical scanning tunneling microscopy (EC-STM) was used to obtain images of the self-assembled monolayer with molecular resolution. Potential-assisted assembly of β-Tg onto a Au(111) electrode surface was found to be complicated by oxidation of β-Tg molecules. The EC-STM images revealed formation of a passive layer containing honeycomb-like domains characteristic of a formation of S(8) rings, indicating the S-C bond may have been cleaved. In contrast, passive self-assembly of thioglucose from a methanol solution was found to produce a stable, disordered monolayer of β-Tg. Since the passive assembly method was not complicated by the presence of a faradaic process, it is the method of choice for modifying the gold surface with a hydrophilic monolayer.     

An adeno-associated viral vector transduces the rat hypothalamus and amygdala more efficient than a lentiviral vector

Background  

This study compared the transduction efficiencies of an adeno-associated viral (AAV) vector, which was pseudotyped with an AAV1 capsid and encoded the green fluorescent protein (GFP), with a lentiviral (LV) vector, which was pseudotyped with a VSV-G envelop and encoded the discosoma red fluorescent protein (dsRed), to investigate which viral vector transduced the lateral hypothalamus or the amygdala more efficiently. The LV-dsRed and AAV1-GFP vector were mixed and injected into the lateral hypothalamus or into the amygdala of adult rats. The titers that were injected were 1 × 10⁸ or 1 × 10⁹ genomic copies of AAV1-GFP and 1 × 10⁵ transducing units of LV-dsRed.     

Entropy and Ergodicity of Boole-Type Transformations

We review some analytic, measure-theoretic and topological techniques for studying ergodicity and entropy of discrete dynamical systems, with a focus on Boole-type transformations and their generalizations. In particular, we present a new proof of the ergodicity of the 1-dimensional Boole map and prove that a certain 2-dimensional generalization is also ergodic. Moreover, we compute and demonstrate the equivalence of metric and topological entropies of the 1-dimensional Boole map employing “compactified”representations and well-known formulas. Several examples are included to illustrate the results. We also introduce new multidimensional Boole-type transformations invariant with respect to higher dimensional Lebesgue measures and investigate their ergodicity and metric and topological entropies.