Characterization of the mitochondrial processing peptidase of Neurospora crassa

The mitochondrial processing peptidase (MPP) of Neurospora crassa is constituted by an alpha- and a beta-subunit. We have purified alpha-MPP after expression in Escherichia coli while beta-MPP was purified from mitochondria. A fusion protein between precytochrome b2 and mouse dihydrofolate reductase was expressed in E. coli, and the purified protein was used as substrate for MPP. Both subunits of MPP are required for processing. MPP removes the matrix targeting signal of cytochrome b2 by a single cut, and the resulting presequence peptide is 31 amino acid residues in length. It acts as a competitive inhibitor of processing but has a approximately 30-fold lower affinity for MPP than the preprotein. Competition assays show that MPP recognizes the COOH- terminal portion of the presequence of cytochrome b2 rather than the NH2-terminal part which has the potential to form an amphiphilic helix. Substitution of arginine in position -2 of the matrix targeting sequence of cytochrome b2 prevents processing but not import of a chimeric precursor. Substitution of the tyrosyl residue in position +1 also prevents processing, indicating that MPP interacts with sequences COOH-terminal to the cleavage site. Non-cleavable preprotein is still recognized by MPP. Our data suggest that processing peptidase and import machinery recognize distinct structural elements in preproteins which, however, can be overlapping

Single hole dynamics in the one dimensional t-J model

We present a new finite-temperature quantum Monte Carlo algorithm to compute imaginary-time Green functions for a single hole in the t-J model on non-frustrated lattices. Spectral functions are then obtained with the Maximum Entropy method. Simulations of the one-dimensional case show that a simple charge-spin separation Ansatz is able to describe the overall features of the spectral function over the whole energy range for values of J/t from 1/3 to 4. This includes the bandwidth W \sim 4t + J and the compact support of the spectral function. The quasiparticle weight Z_k is computed on lattices up to L=96 sites, and scales as Z_k\propto L^{-1/2}.Comment: 8 pages, 5 figure

D-branes on the Quintic

We study D-branes on the quintic CY by combining results from several directions: general results on holomorphic curves and vector bundles, stringy geometry and mirror symmetry, and the boundary states in Gepner models recently constructed by Recknagel and Schomerus, to begin sketching a picture of D-branes in the stringy regime. We also make first steps towards computing superpotentials on the D-brane world-volumes.Comment: harvmac, 78 pp (v3: notes added and improved discussion of an example

Ready-meal consumption: associations with weight status and cooking skills

Objective:The ready-meal market has grown considerably in recent years. Atthe same time, a degradation of traditional cooking skills has been observed.Ready meals are often rich in energy, fat and sugar and lack vegetables; however,studies investigating associations between ready-meal consumption, overweightand cooking skills are lacking. The present study examines whether demographicfactors, overweight, beliefs about the nutritional value and taste of ready mealsand cooking skills are associated with ready-meal consumption.Design:Cross-sectional survey.Setting:Ready-meal consumption, weight status, cooking skills, beliefs aboutthe taste and nutritional value of ready meals and demographic variables wereassessed with self-administered questionnaires. Data were analysed with one-wayANOVA and multiple regression analysis.Subjects:A total of 1017 adults from the German-speaking part of Switzerland.Results:Men reported being more positive about ready meals and havingfewer cooking skills compared with women. Overweight adults (BMI.25 kg/m2)were more positive about nutrients and vitamins in ready meals compared withnormal-weight adults. Ready-meal consumption was associated with cooking skills(b520?192), age (b520?228), overweight (b50?129), nutritional value (b520?131), taste (b520?126), working status (b50?096) and gender (b50?084).Conclusions:Cooking skills were identified as a strong predictor of ready-mealconsumption. The importance of cooking skills as a barrier to healthy eatingshould be explored, as it is plausible that cooking skills will further decrease in thefuture. Next, the study provided evidence for an association between ready-mealconsumption and overweight. Further research should examine the importance ofready meals for the overweight epidemic