Protein import into yeast mitochondria is accelerated by the outer membrane protein MAS70.

The yeast mitochondrial outer membrane contains a major 70 kd protein with an amino-terminal hydrophobic membrane anchor and a hydrophilic 60 kd domain exposed to the cytosol. We now show that this protein (which we term MAS70) accelerates the mitochondrial import of many (but not all) precursor proteins. Anti-MAS70 IgGs or removal of MAS70 from the mitochondria by either mild trypsin treatment or by disrupting the nuclear MAS70 gene inhibits import of the F1-ATPase beta-subunit, the ADP/ATP translocator, and of several other precursors into isolated mitochondria by up to 75%, but has little effect on the import of porin. Intact cells of a mas70 null mutant import the F1-ATPase alpha-subunit and beta-subunits, cytochrome c1 and other precursors at least several fold more slowly than wild-type cells. Removal of MAS70 from wild-type mitochondria inhibits binding of the ADP/ATP translocator to the mitochondrial surface, indicating that MAS70 mediates one of the earliest import steps. Several precursors are thus imported by a pathway in which MAS70 functions as a receptor-like component. MAS70 is not essential for import of these precursors, but only accelerates this process.     

The role of microtubules and cell-wall deposition in elongation of regenerating protoplasts of Mougeotia

Protoplasts of the filamentous green alga Mougeotia sp. are spherical when isolated and revert to their normal cylindrical cell shape during regeneration of a cell wall. Sections of protoplasts show that cortical microtubules are present at all times but examination of osmotically ruptured protoplasts by negative staining shows that the microtubules are initially free and become progressively cross-bridged to the plasma membrane during the first 3 h of protoplast culture. Cell-wall microfibrils areoobserved within 60 min when protoplasts are returned to growth medium; deposition of microfibrils that is predominantly transverse to the future axis of elongation is detectable after about 6 h of culture. When regenerating protoplasts are treated with either colchicine or isopropyl-N-phenyl carbamate, drugs which interfere with microtubule polymerization, they remain spherical and develop cell walls in which the microfibrils are randomly oriented.     

Microbial Metal Tolerance in Bermuda Carbonate Sediments

The recovery of aerobic heterotrophic bacteria from Bermuda carbonate sediments on metal-supplemented media varied as much as 44-fold over a 15-cm depth. Distributional relationships with sulfate-reducing bacteria and sediment character indicated that metal tolerance was a function of metal bioavailability.     

Anti-P autoantibody production requires P1/P2 as immunogens but is not driven by exogenous self-antigen in MRL mice

Considerable evidence supports the idea that autoantibody production in human and murine SLE is Ag driven. To determine whether Ag (the ribosomal P proteins) could initiate autoantibody production in lupus mice, 34 MRL/lpr mice were immunized with mouse riboosomal proteins in Freund's adjuvant. Neither intact ribosomes, denatured total mouse ribosomal proteins, nor the purified mouse ribosomal proteins, P1 and P2, induced the production of anti-P autoantibodies in the MRL/lpr mice. In contrast to these negative findings, MRL/lpr mice immunized with Artemia salina ribosomes produced anti-P antibodies as well as anti-P autoantibodies. Although the induced anti-P autoantibodies bound exclusively to the carboxyl terminus, these anti-P antibodies differed from spontaneously occurring anti-P autoantibodies in their predominant binding to mouse P0 on immunoblots and their preferential reactivity against A. salina synthetic peptides by ELISA. Induction of anti-P antibodies required the presence of P1 and P2 on the ribosome because ribosomal cores devoid of P1 and P2 dimers did not induce anti-P. Despite the presence of approximately 80 ribosomal proteins, autoantibodies to other mouse ribosomal proteins were rarely observed. Immunization of MRL/+ mice and a normal H-2-matched strain of mice, C3H, also resulted in anti-P antibodies reactive with the A. salina P proteins and mouse P0. Whereas anti-P levels gradually declined in C3H mice, anti-P levels either remained elevated (MRL/lpr) or showed a secondary rise (MRL/+) at the onset of autoimmunity. These observations indicate that: i) high levels of autologous Ag are not sufficient to drive antiribosomal autoantibody production in MRL mice, ii) multivalency of the P proteins may explain their potent immunogenicity and ability to break tolerance, and iii) immunized MRL mice show an abnormal persistence of high level anti-P production presumably reflecting T cell activation of presensitized B cells.     

Follicle-stimulating hormone pulse amplitude decreases with the onset of the breeding season in the mare

The relationship between daily mean FSH concentrations in serum and the pattern of FSH detected by frequent sampling for 12-h periods (samples every 15 min) was examined in five mares during the transition into the breeding season. The five mature anestrous mares were exposed to a natural increase in daylength. Blood samples were collected daily from February 1 until the first ovulation of the breeding season (April 14 +/- 3.7 days, Mean +/- SEM). Periods of frequent blood collection were performed every two weeks. Blood samples were obtained daily by jugular venipuncture or jugular cannula (frequent samples). Mean daily concentrations of FSH in serum determined by RIA decreased during seasonal transition. Patterns of FSH in serum detected by frequent sampling were pulsatile. FSH pulse amplitude decreased during seasonal transition, and the decrease in amplitude was associated with the decrease in mean serum FSH concentrations. This decrease in FSH pulse amplitude may reflect an involvement of a follicular product from developing follicles or a change in hypothalamic stimulation of pituitary FSH release.     

The effect of two proteinase inhibitors, E-64 and the Bowman-Birk inhibitor, on the developmental time and mortality of Acanthoscelides obtectus

An artificial bean seed system was used to evaluate the effects of a cysteine proteinase inhibitor (E-64) and a serine proteinase inhibitor (Bowman-Birk inhibitor) on the developmental time and mortality of the common bean weevil, Acanthoscelides obtectus (Say). These inhibitors were incorporated into artificial bean seeds on which the insect fed. To better understand the mode of action of these inhibitors, free amino acids were also added to the seeds, alone and in combination with the inhibitors. E-64 was found to be highly effective in delaying development and increasing mortality of the insect. Both effects were directly related to the concentration of E-64. Bowman-Birk inhibitor had little effect on these parameters. Assays of gut proteolytic activity of insects reared on artificial seeds with various levels of E-64 demonstrated a direct relationship between E-64 concentration in the diet and reduction of gut proteolytic activity. Free amino acid supplementation to the diet did not prevent inhibition of gut proteolytic activity by E-64, but did reverse its effects on developmental time and mortality, strengthening the hypothesis that E-64 operates by inhibition of essential digestive proteinase activity.

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Résumé Des grains artificiels de haricot ont été utilisés pour évaluer les effets sur la durée de développement et la mortalité d' Acanthoscelides obtectus. Say d'inhibiteurs de la protéinase de la cystéine (E-64) et de la protéinase de la sérine (l'inhibiteur de Bowman-Birk). Ces inhibiteurs avaient été incorporés dans les grains artificiels. Pour mieux comprendre leur voie d'action, des acides aminés libres étaient ajoutés à ces graines, seuls ou combinés aux inhibiteurs. E-64 a très efficacement retardé le développement et accru la mortalité; ces 2 effets étaient liés à sa concentration. L'inhibiteur de Bowman-Birk a eu peu d'effets sur ces paramètres. Des expériences sur l'activité protéolytique du tube digestif d'insectes élevés sur des graines artificielles avec différentes concentrations de E-64 ont montré une relation directe entre la concentration en E-64 et la réduction de l'activité protéolytique. L'addition d'acides aminés libres dans l'aliment n'a pas empêché l'inhibition de l'activité protéolytique par E-64, mais a inversé ses effets sur la durée de développement et la mortalité, renforçant l'hypothèse que E-64 agit en inhibant l'activité protéinase digestive essentielle.

     

Spontaneous regression of Friend virus-induced erythroleukemia. VI. Structural and antigenic differences between the regressing and conventional strains of virus.

The regressing and conventional strains of Friend virus were compared by neutralization assays, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and tryptic peptide mapping of the individual viral components. Neutralization rates of the two viruses differed in the presence of monospecific anti-gp70 antiserum and sera from regressed or immunized mice. Neutralization of regressing Friend virus, but not conventional Friend virus, occurred when the viruses were incubated with anti-p15(E) and complement. Human serum inactivated conventional Friend virus more rapidly than regressing Friend virus, probably as a result of virolysis induced by the reaction of viral p15(E) with human complement component C1. Structural differences between the viruses were detected in their gp70 viral glycoproteins and p15(E) and p12 proteins. Analysis of different stocks and clonal isolates of the viruses showed that the differences between the gp70 and p15(E), but not the p12 proteins, were associated with the regressing phenotype of the regressing strain of Friend virus.     

Bend propagation in flagella. I. Derivation of equations of motion and their simulation.

A set of nonlinear differential equations describing flagellar motion in an external viscous medium is derived. Because of the local nature of these equations and the use of a Crank-Nicolson-type forward time step, which is stable for large deltat, numerical solution of these equations on a digital computer is relatively fast. Stable bend initiation and propagation, without internal viscous resistance, is demonstrated for a flagellum containing a linear elastic bending resistance and an elastic shear resistance that depends on sliding. The elastic shear resistance is derived from a plausible structural model of the radial link system. The active shear force for the dynein system is specified by a history-dependent functional of curvature characterized by the parameters m0, a proportionality constant between the maximum active shear moment and curvature, and tau, a relaxation time which essentially determines the delay between curvature and active moment.     

Spatial co‐localisation of extreme weather events: a clear and present danger

Extreme weather events have become a dominant feature of the narrative surrounding changes in global climate with large impacts on ecosystem stability, functioning and resilience; however, understanding of their risk of co‐occurrence at the regional scale is lacking. Based on the UK Met Office’s long‐term temperature and rainfall records, we present the first evidence demonstrating significant increases in the magnitude, direction of change and spatial co‐localisation of extreme weather events since 1961. Combining this new understanding with land‐use data sets allowed us to assess the likely consequences on future agricultural production and conservation priority areas. All land‐uses are impacted by the increasing risk of at least one extreme event and conservation areas were identified as the hotspots of risk for the co‐occurrence of multiple event types. Our findings provide a basis to regionally guide land‐use optimisation, land management practices and regulatory actions preserving ecosystem services against multiple climate threats.