A fast dynamic mode of the EF‐G‐bound ribosome

A key intermediate in translocation is an ‘unlocked state’ of the pre‐translocation ribosome in which the P‐site tRNA adopts the P/E hybrid state, the L1 stalk domain closes and ribosomal subunits adopt a ratcheted configuration. Here, through two‐ and three‐colour smFRET imaging from multiple structural perspectives, EF‐G is shown to accelerate structural and kinetic pathways in the ribosome, leading to this transition. The EF‐G‐bound ribosome remains highly dynamic in nature, wherein, the unlocked state is transiently and reversibly formed. The P/E hybrid state is energetically favoured, but exchange with the classical P/P configuration persists; the L1 stalk adopts a fast dynamic mode characterized by rapid cycles of closure and opening. These data support a model in which P/E hybrid state formation, L1 stalk closure and subunit ratcheting are loosely coupled, independent processes that must converge to achieve the unlocked state. The highly dynamic nature of these motions, and their sensitivity to conformational and compositional changes in the ribosome, suggests that regulating the formation of this intermediate may present an effective avenue for translational control.     

Studies on ulcerative dermal necrosis of salmonids

Fourteen fresh run salmon Satmo salar L. with early extant lesions of ulcerative dermal necrosis (UDN) were kept in separate tanks and treated with zinc free malachite green. Ten of the fish were held at 10° C and 4 at 2° C. The treatment precluded infection with Saprolegnia fungus and allowed natural resolution of the lesions. There was a marked difference in rate of healing between warm and cold water conditions.
Histological examination of healing lesions at different stages showed that there was a primary invasion of cuboidal epithelium over the collagen scar followed by a phase of disorganized proliferation which eventually organized itself into normal epithelium. Melanocytes were very obvious in the dermis of healing lesions.     

Translational control during the acute phase response. Ferritin synthesis in response to interleukin-1.

Interleukin-1 (IL-1 beta) increases the synthesis of both heavy and light (L)-ferritin subunits when added to human hepatoma cells (HepG2) grown in culture. RNase protection and Northern blot analysis with L-ferritin probes revealed that no changes in L-ferritin mRNA levels occur after cytokine stimulation. However, the induction coincides with an increased association of the L-subunit mRNA with polyribosomes. Since the recruitment of stored ferritin mRNA onto polyribosomes is seen when iron enters the cell, the effect of IL-1 beta on iron uptake was tested and was found to be unaffected by the lymphokine. Neither transferrin receptor mRNA levels nor the number of receptors displayed on the cell surface was affected by IL-1 beta. However, the action of the cytokine on ferritin translation is inhibited by the action of the intracellular iron chelator deferoxamine. These data indicate that IL-1 beta induces ferritin gene expression by translational control of its mRNA. The pathway of induction is different from iron-dependent ferritin gene expression whereas regulation requires the background presence of cellular iron.     

Identification of major common extracellular proteins secreted by Aeromonas salmonicida strains isolated from diseased fish.

Ten different strains of Aeromonas salmonicida that were isolated from diseased fish were grown under identical conditions (24 h at 25 degree C) in 3% (wt/vol) tryptone soya broth medium supplemented with vitamins and inorganic ions. In each case the extracellular proteins that were formed were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it was found that there were two significant common components, one with a molecular weight of 70,000 and the other with a weight of 56,000. Application of enzyme purification techniques to the supernatant fraction proteins of a culture of one of the strains resulted in the isolation of a 70-kilodalton (kDa) component, which was found to be a serine protease, and a 56-kDa component, which was hemolytic to trout erythrocytes. Rocket immunoelectrophoresis with rabbit antibodies to the isolated protease and hemolysin showed the same antigenic components in the supernatant fractions of all the cultures. These activities were assayed, and protease activity was found to vary by a factor of three, from 59 to 195 U/ml, while the range of hemolytic activity was over a narrow band, from 28 to 43 U/ml. There was an inconsistency between the immunoelectrophoretic and direct assay data in only one case. This indicated the presence of additional hemolytic activity, in addition to the 56-kDa component. The detection of large amounts of the same protease and hemolysin, two potent degradative activities, in a random series of strains of A. salmonicida suggests that they may be obligatory virulence factors in the development of furunculosis.     

Effect of microorganisms on rate of liquid extraction of ethanol from fermentation broths

Liquid extraction is one means of removing metabolic products continuously during a fermentation and so reducing product inhibition. It is known that microbial organisms are attracted to liquid-liquid interfaces, and it is important for the design of extraction systems to establish if this has a detrimental effect on the rate of extraction. The extraction of ethanol from aqueous suspensions of yeast (Saccharomyces cerevisiae) using n- decanol is described in this paper. It was found that the presence of the yeast cells severely reduced the rate of ethanol extraction. The overall mass transfer coefficient was reduced from 5.0 x 10(-6) to 0.7 x 10(-6) m/s. This reduced overall mass transfer coefficient was unaffected by yeast concentration in the range 0.1-20 kg/m(3). The results are consistent with the yeast cells adsorbing to the interface in closely packed layers and preventing mass transfer by simply reducing the available interfacial area. Optical microscope observations confirmed that a yeast layer several cell diameters thick rapidly built up at the interface when a small decanol droplet was added to a yeast suspension.     

Studies of heterogeneous mitochondrial populations in a mouse cell line: the effects of selection for or against mitochondrial genomes that confer chloramphenicol resistance

A single nucleotide substitution in a highly conserved region of the mitochondrial genome of a mouse cell line confers both chloramphenicol resistance and an alteration to the recognition site for the endonuclease Eco RV. This has enabled a detailed study on the effects of selection on a mitochondrial population comprising initially both chloramphenicol-resistant and chloramphenicol-sensitive mitochondrial genomes. The mutation confers advantage to cells grown in the presence of chloramphenicol, but is apparently deleterious in its absence. Selection at the cellular level is sufficient to explain the results observed. Fixation, which results in cells having mitochondria of only a single type, is slow. It is probable, therefore, that mammalian oocyte mitochondria are derived from only a small number of progenitors. This would allow fixation of new mutations and explain the observed uniformity in mitochondrial genomes of the individual in the presence of extensive variation between different members of the population.     

Simultaneous total correction of temporomandibular ankylosis and facial asymmetry

Ankylosis of the temporomandibular joint not only prevents mouth opening and chewing, but also affects the growth and position of the mandible. This produces progressive facial distortion with devastating psychosocial effects compounding the already difficult problem of not being able to open the mouth. Over the past 6 years, 18 patients in Canada and Taiwan were treated by excision of a large block of bone at the ankylosis and repositioning of the jaw, with the addition of osteotomies as necessary to produce a symmetrical face with good occlusion. Bilateral cases were treated at one operation in a similar way. The temporomandibular joint and absent ramus were constructed with a costochondral graft taken from the opposite chest. Some patients were treated with intermaxillary fixation for 8 weeks, while others had no fixation, but there was no difference in the effectiveness of correction of the ankylosis.