Protein translocation at the ER membrane: A complex process becomes more so

Protein transport across or insertion into a membrane is facilitated by multicomponent protein complexes that reside in the bilayer. Current models propose that these complexes mediate translocation and integration by an obligate sequence of interactions between the substrate polypeptide and other components. Recent discoveries extend and complicate these models, but, more importantly, they remind us that our current level of understanding of the actual molecular mechanisms involved is crude and represents only the tip of the iceberg.     

Patterns of shortening and thickening of the human diaphragm

Wait, J. L., and R. L. Johnson. Patterns of shorteningand thickening of the human diaphragm. J. Appl.Physiol. 83(4): 1123-1132, 1997.To study how the human diaphragm changesconfiguration during inspiration, we simultaneously measured diaphragmthickening using ultrasound and inspired volumes using apneumotachograph. Diaphragm length was assessed by chest radiography.We found that thickening and shortening were greatest during a breathtaken primarily with the abdomen. However, the degree of thickening wasgreater than expected for fiber shortening, assuming parallel musclefibers and no shear. So, to clarify this unexpected finding, weconsidered geometric models of the diaphragm. How a muscle thickens asits fibers shorten is critically dependent on geometry. Thus, if a flatrectangular sheet of muscle shortens along one dimension, surfacearea-to-length ratio along this dimension should remain constant, andthickness would be inversely proportional to length during shortening.The simplest model of the diaphragm, however, is a cylindrical sheet ofmuscle in the zone of apposition capped by a dome; the ratio of surfacearea to radial fiber length in the dome is substantially less than theratio of area to length of the cylindrical zone of apposition; hence,as the zone of apposition shortens while the dome radius remainsconstant, the ratio of total surface area to combined length (i.e.,dome + zone of apposition) must decrease and thickening of the musclecorrespondingly must increase more than expected for a simplerectangular strip. A similar relationship can be derived betweenthickening and length in a muscle sheet with a wedge-shaped insertioninto a thin flat tendon. Comparison of calculations with these types ofmodels to data from human subjects indicates that the unexpectedthickening in the zone of apposition is explained by the peculiargeometry of the diaphragm. The greater thickening of the diaphragm inthe zone of apposition suggests that more of the muscle mass and more sarcomeres are retained in the zone of apposition as the dome descends.Physiologically, this greater thickening may have importance byreducing wall stress in the zone of apposition and reducing the work orenergy requirements per sarcomere.

     

The cosmid CSSM25 assigns syntenic group U2 to bovine Chromosome 9 and is localized to ovine Chromosome 8

The cosmid-derived microsatellite CSSM 25 has previously been shown to map to bovine syntenic group U2 by link-age and hybrid somatic cell analysis. We have mapped the cosmid by fluorescent in situ hybridization to bovine Chromosome (Chr) 9q17-21 and ovine Chr 8q17-21 and hence assign U2 to Chr 9 in cattle. Bovine Chr 9 and ovine Chr 8 show strong banding pattern homology, and the localization of CSSM 25 to the same region confirms the strong conservation of gene locations on these chromosomes.     

Effects of Simulated Rain on the Persistence of Beauveria bassiana Conidia on Leaves of Alfalfa and Wheat

The effect of simulated rain at two intensities (26.7 or 112.7 mm h-1) and durations (30 or 60 min) on the persistence of Beauveria bassiana conidia applied in water on leaves of alfalfa leaves of alfalfa (Medicago sativa) or wheat (Triticum aestivum) was investigated. Initial populations of conidia on the leaves of both crops were similar, and ranged from 1.7 105 to 3.5 105 colony-forming units cm-2. The simulated rain reduced the concentration of conidia on leaves by 28-61%. Although there was a slight effect due to rain intensity for alfalfa, there was no influence of either rain duration or crop type on the retention of B. bassiana conidia.     

SAR in rats exposed in 2,450-MHz circularly polarized waveguides

Average specific absorption rates (SARs) for live rats exposed in 2,450-MHz circularly polarized waveguides were estimated from the total system loss determined from measurements using five power meters, and a correction factor representing actual SAR/apparent SAR. The actual SAR was measured by twin-well calorimetry and the apparent SAR by power meters. Values were obtained for carcasses of various body masses for five orientations. The average SAR with free movement in the cages changed less than threefold as the rats grew from 200 to 700 g. The ratio of peak to average SAR in the body was less than 3. These results indicate relatively constant energy disposition in rats exposed in the circularly polarized waveguide.     

The polyadenylated RNA of zoospores and growth phase cells of the aquatic fungus,Blastocladiella

The stored poly(A) + RNA from zoospores of the aquatic fungus Blastocladiella emersonii represents 2.5% of the total RNA and has a model MW of 425,000 daltons and an average poly(A) isostich of 32 bases. The poly(A) + RNA also represents 2.5% of the total RNA from early growth phase cells and has a modal MW of 360,000 daltons and an average poly(A) isostich of 38 bases. The poly(A) + RNA from spores and 2-hr plants contains a structure resistant to RNases T₁, T₂, and A, which can be labeled with ³²PO₄ and which will bind to DBAE-cellulose. These characteristics strongly suggest that both the zoospore poly(A) + RNA and the 2-hr cell poly(A) + RNA are capped at the 5′ end; and, hence, it is unlikely that capping is involved in the control of protein synthesis during germination.Approximately 80% of the poly(A) + RNA of the spore is located in the membrane-enclosed ribosomal nuclear cap, and more than 90% of the poly(A) + RNA within the cap is found in the 80S monoribosome and heavier fractions.Synthesis of new poly(A) + RNA occurs very early during zoospore germination, and the labeled poly(A) + RNA rapidly enters the newly organized polysomes. The labeling data for early germination also suggest that cytoplasmic polyadenylation occurs.     

Carbohydrate composition of variant-specific surface antigen glycoproteins from Trypanosoma brucei

The carbohydrate of variant-specific surface antigen glycoproteins from bloodstream forms of 13 cloned variants of Trypanosoma brucei was analyzed by gas-liquid chromatography. The glycoproteins contained from 6 to 17% carbohydrate by weight, and all contained the same 4 sugars: mannose, galactose, glucose, and glucosamine (probably as N-acetylglucosamine). The glycoprotein from variant 048, strain 427 contained (+20%) 11 mannose, 4 galactose, 4 glucose, and 5 glucosamine residues/mole of glycoprotein (molecular weight 65,000). Glucose was an intergral component of the glycoproteins, not dissociable by sodium dodecyl sulphate, 8 M urea, or 1 M acetic acid. Some of the glucose was dissociated by trichloroacetic acid. Most of the glycoproteins formed precipitin with concanavalin A in Ouchterlony double diffusion, but none formed such bands with wheat germ agglutinin or Ricinus communis lectin (molecular weight 120, 000).     

Schizophrenia and reduced cyclic AMP production: evidence for the role of receptor-linked events

Reduced cyclic AMP (cAMP) production has been found in platelets of schizophrenic patients. cAMP is generated physiologically as a result of a series of steps beginning with receptor activation by a ligand, progressing through activation of the enzyme protein, adenylate cyclase. The deficit of cAMP found in the schizophrenic population may occur at any one, or at multiple steps in this cascade. The present study attempts to discriminate whether impaired adenylate cyclase itself was responsible for the cAMP deficit or whether abnormalities in receptor events or linkage are present in schizophrenics. The production of cAMP following direct stimulation of adenylate cyclase by NaF was contrasted with receptor mediated activation of adenylate cyclase by prostaglandin E1 (PGE1) in disrupted platelet preparations from schizophrenics and normal controls. cAMP formation stimulated by NaF was not different in platelets of schizophrenics as compared to controls, however, platelets of schizophrenics showed reduced response to PGE1 stimulation. The authors interpret these findings as evidence for a membrane associated abnormality of either receptor or receptor-adenylate cyclase linkage in the schizophrenias.