Zur Characteristik gewisser Botaniker

Ohne Zusammenfassung     

Corrections to the Saffman-Delbruck mobility for membrane bound proteins

Recent experiments (Gambin, Y., R. Lopez-Esparza, M. Reffay, E. Sierecki, N. S. Gov, M. Genest, R. S. Hodes, and W. Urbach. 2006. Proc. Natl. Acad. Sci. USA. 103:2098-2102) have called into question the applicability of the Saffman-Delbrück diffusivity for proteins embedded in the lipid bilayers. We present a simple argument to account for this observation that should be generically valid for a large class of transmembrane and membrane bound proteins. Whenever the protein-lipid interactions locally deform the membrane, that deformation generates new hydrodynamic stresses on the protein-membrane complex leading to a suppression of its mobility. We show that this suppression depends on the protein size in a manner consistent with the work of Gambin et al.     

Data rotation improves genomotyping efficiency

Unsequenced bacterial strains can be characterized by comparing their genomic DNA to a sequenced reference genome of the same species. This comparative genomic approach, also called genomotyping, is leading to an increased understanding of bacterial evolution and pathogenesis. It is efficiently accomplished by comparative genomic hybridization on custom-designed cDNA microarrays. The microarray experiment results in fluorescence intensities for reference and sample genome for each gene. The log-ratio of these intensities is usually compared to a cut-off, classifying each gene of the sample genome as a candidate for an absent or present gene with respect to the reference genome. Reducing the usually high rate of false positives in the list of candidates for absent genes is decisive for both time and costs of the experiment. We propose a novel method to improve efficiency of genomotyping experiments in this sense, by rotating the normalized intensity data before setting up the list of candidate genes. We analyze simulated genomotyping data and also re-analyze an experimental data set for comparison and illustration. We approximately halve the proportion of false positives in the list of candidate absent genes for the example comparative genomic hybridization experiment as well as for the simulation experiments.     

Moraxella catarrhalis is only a weak activator of the mannose-binding lectin (MBL) pathway of complement activation

A hemolytic bystander assay was used to assess the functional serum mannose-binding lectin (MBL) activating capacity of five isolates of Moraxella catarrhalis obtained from children who suffered recurrent acute otitis media episodes. Results showed that this organism is only a poor activator of the lectin pathway of complement activation, with subsequent consequences for the etiology of otitis media by this organism.     

Efficient gene inactivation in Bacillus anthracis

A procedure for high-efficiency gene inactivation in Bacillus anthracis has been developed. It is based on a highly temperature-sensitive plasmid vector carrying kanamycin resistance cassette surrounded by DNA fragments flanking the desired insertion site. The approach was tested by constructing glutamate racemase E1 (racE1), glutamate racemase E2 (racE2) and comEC knock-out mutants of B. anthracis strain DeltaANR. Allelic replacements were observed at high frequencies, ranging from approximately 0.5% for racE2 up to 50% for racE1 and comEC. The system can be used for genetic validation of potential drug targets.     

Rapid functional assays of recombinant IP3 receptors

Functional assays of inositol 1,4,5-trisphosphate receptors (IP3R) currently use 45Ca2+ release methods, fluorescent Ca2+ indicators within either the ER or cytosol, or electrophysiological analyses of IP3R in the nuclear envelope or artificial bilayers. None of the methods is presently amenable to the rapid, high-throughput quantitative analyses of IP3R function needed to address the structural determinants of IP3R behavior. We use a low-affinity Ca2+ indicator (Mag-fluo-4) to measure free [Ca2+] within the ER of permeabilized DT40 cells expressing only rat type 1 IP(3)R, and establish that the indicator is capable of reliably reporting the Ca(2+) release evoked by IP3. A 96-well fluorescence plate reader equipped for automated fluid additions (FlexStation, Molecular Devices) is used to monitor IP3-evoked Ca2+ release. The method allows quick and economical functional assays of recombinant IP3R in small volumes (< or = 100 microl).     

Whole-genome shotgun optical mapping of Rhodospirillum rubrum

Rhodospirillum rubrum is a phototrophic purple nonsulfur bacterium known for its unique and well-studied nitrogen fixation and carbon monoxide oxidation systems and as a source of hydrogen and biodegradable plastic production. To better understand this organism and to facilitate assembly of its sequence, three whole-genome restriction endonuclease maps (XbaI, NheI, and HindIII) of R. rubrum strain ATCC 11170 were created by optical mapping. Optical mapping is a system for creating whole-genome ordered restriction endonuclease maps from randomly sheared genomic DNA molecules extracted from cells. During the sequence finishing process, all three optical maps confirmed a putative error in sequence assembly, while the HindIII map acted as a scaffold for high-resolution alignment with sequence contigs spanning the whole genome. In addition to highlighting optical mapping's role in the assembly and confirmation of genome sequence, this work underscores the unique niche in resolution occupied by the optical mapping system. With a resolution ranging from 6.5 kb (previously published) to 45 kb (reported here), optical mapping advances a "molecular cytogenetics" approach to solving problems in genomic analysis.     

Influence of exercise order on the number of repetitions performed and perceived exertion during resistance exercises

This study examined the performance effects of exercise order during a resistance-training session composed of only upper-body exercises. The 10 repetition maximum of 14 men and 4 women with at least 6 months of previous weight-training experience was determined for 5 upper-body exercises. Each subject then completed 2 training sessions separated by 48 hours in a counterbalanced crossover design. One session began with exercises of the large-muscle group and progressed to exercises of the small-muscle group (sequence A), whereas the other session was performed with the opposite exercise sequence (sequence B). The exercise order for sequence A was free-weight bench press (BP), machine lat pull-down (LPD), seated machine shoulder press (SP), standing free-weight biceps curl (BC) with a straight bar, and seated machine triceps extension (TE). The exercise order for sequence B was TE, BC, SP, LPD, and BP. During both sequences, 3 sets of each exercise were performed to concentric failure, with 2-minute recovery intervals between sets and exercises. Performing exercises of both the large- and the small-muscle groups at the end of an exercise sequence resulted in significantly fewer repetitions in the 3 sets of an exercise. This decrease in the number of repetitions performed was especially apparent in the third set when an exercise was performed last in an exercise sequence.