Analysis of an activatable promoter: sequences in the simian virus 40 late promoter required for T-antigen-mediated trans activation.

The late promoter of simian virus 40 (SV40) is activated in trans by the viral early gene product, T antigen. We inserted the wild-type late-promoter region, and deletion mutants of it, into chloramphenicol acetyltransferase transient expression vectors to identify promoter sequences which are active in the presence of T antigen. We defined two promoter activities. One activity was mediated by a promoter element within simian virus 40 nucleotides 200 to 270. The activity of this element was detectable only in the presence of an intact, functioning origin of replication and accounted for 25 to 35% of the wild-type late-promoter activity in the presence of T antigen. The other activity was mediated by an element located within a 33-base-pair sequence (simian virus nucleotides 168 to 200) which spans the junction of the 72-base-pair repeats. This element functioned in the absence of both the origin of replication and the T-antigen-binding sites and appeared to be responsible for trans-activated gene expression. When inserted into an essentially promoterless plasmid, the 33-base-pair element functioned in an orientation-dependent manner. Under wild-type conditions in the presence of T antigen, the activity of this element accounted for 65 to 75% of the late-promoter activity. The roles of the 33-base-pair element and T antigen in trans-activation are discussed.     

Are Chaoborus larvae more abundant in acidified than in non-acidified lakes in Central Canada?

Eriksson et al (1980) hypothesized that the abundance of certain macroinvertebrate predators, such as larvae of the phantom midge Chaoborus , should increase in acidified lakes because of the elimination of fish. To examine the influence of pH and presence of fish on Chaoborus abundance, we surveyed Chaoborus populations in 33 lakes in Ontario, Canada which ranged in pH from 4.5 to 7.4. Chaoborus larvae were not more abundant in the acidified lakes that were devoid of fish than in the remaining lakes. Therefore, we concluded that pH and presence of fish are not prime determinants of total Chaoborus abundance in Canadian Shield lakes. We hypothesized that significant increases in Chaoborus abundance should only be anticipated when fish populations are eliminated by acidification of relatively nutrient rich lakes.     

The influence of a fall fumigation with ozone on the stomatal behavior of spruce and fir

Summary Clonal stock (grafts of 15-, 50-, and 100-year-old trees) of spruce (Picea abies (L.) Karst.) and fir (Abies alba Mill.) was exposed either to 150 ppb ozone (300 gm^-3) during 9 daylight hours or to carbon-filtered air on 35 days between 29 August and 21 October 1983. At the end of the fumigation the trees did not exhibit any visible signs of injury. Transpiration and leaf conductance in light and darkness, measured with a Licor porometer, revealed, however, stomatal sluggishness and — in spruce-increased transpiration.     

Dolichol and Dolichyl Phosphate Levels in Brain Tissue from English Setters with Ceroid Lipofuscinosis

Human ceroid lipofuscinosis (CL) is an inherited disease marked by cerebromacular degeneration and early death. We have utilized the canine model to investigate the possible role of dolichol and dolichyl phosphate in the developmental pathology of CL. We found that while brain levels of dolichol increase with age in both affected and unaffected dogs, the amount in the diseased animal was similar to that in controls. Brain levels of dolichyl phosphate ranged from 20 to 35 micrograms/g in control dogs at all ages examined, but increased substantially during development in the affected dogs, a value of 113 +/- 24 micrograms/g (mean +/- SD) being obtained in the end-stage animals. In addition to the results obtained in the canine model, dolichyl phosphate levels in human brain tissues from a 5-year-old with late infantile CL and from a 19-year-old with juvenile CL were found to be 153 and 382 micrograms/g, respectively, compared with a control that assayed 26 micrograms/g. The preliminary findings with human tissues provide further evidence for an association of elevated brain dolichyl phosphate levels with CL. Whether the increase is primary or secondary remains to be determined.     

Surface tension gradients: feasible model for gliding motility of Myxococcus xanthus.

We propose that surface tension is the driving force for the gliding motility of Myxococcus xanthus. Our model requires that the cell be able to excrete surfactant in a polar and reversible fashion. We present calculations that (i) estimate the surface tension difference across a cell necessary to move the cell at the observed rate, which is less than 10(-5) dyn/cm, an extremely small value; (ii) estimate the rate of surfactant excretion necessary to produce the required surface tension difference, a rate that we conclude to be metabolically reasonable; (iii) predict the behavior of cells moving in close apposition to each other, and show that the model is consistent with observed behavior; and (iv) predict the behavior of cells moving in dense swarms. In an accompanying paper we present experimental evidence to support the surface tension model.     

Gene mapping and determination of the structure of chloroplast transfer RNA from various photosynthetic organisms

The review sums up data on gene mapping studies of tRNAs of chloroplasts from maize, beans, Euglena, Cyanophora. The mechanisms of splicing of tRNA2Ile from maize chloroplasts and coded for by a gene of unusual length was investigated.     

Studies of protoplast fusion in Streptomyces chrysomallus

Conditions for the regeneration of cells from protoplasts of Streptomyces chrysomallus, a producer of the peptide antibiotic actinomycin, are described. Regeneration of fusion products was most efficient at 27-30 degrees C on regeneration R2 medium (Okanishi et al., 1974) containing 0.25 M-sucrose. The addition of phosphate (150-300 mg 1(-1) to the medium and incubation at 23 degrees C proved to be optimal for the regeneration of individual strains. Highest recombination frequencies after protoplast fusion were obtained by fusing protoplasts in the presence of 45% (w/v) polyethylene glycol 6000. With strains that produce no, or little antibiotic, protoplasts must be present in excess in fusion mixtures in order to overcome inhibition of regeneration by the antibiotic-producing partner.     

Mechanism of depsipeptide formation catalyzed by enniatin synthetase

Covalently bound intermediates of enniatin B synthesis could be isolated from enniatin synthetase by treatment with performic acid. By comparison with products of mild alkaline cleavage of authentic enniatin B they could be identified as the dipeptide D-2-hydroxyisovaleryl-N-methylvaline and the corresponding tetrapeptide. Synthesis of enniatins apparently proceeds via condensation of dipeptides. This was confirmed by the use of the substrate analogue isovaleric acid, which has shown to be a strong inhibitor for enniatin synthesis by formation of N-isovaleryl-N-methyl valine.     

Restricted pH ranges and reduced yields for bacterial growth under pressure

Hydrostatic pressure was found to cause a marked narrowing of pH ranges for growth and reductions in growth yields for a variety of bacteria. In many cases, reduced yields under pressure could be directly related to increased sensitivities to metabolic acids that accumulated in the enclosed culture vessels used. Magnesium and calcium ions partially reversed increases in sensitivities of representative gram-positive and gram-negative bacteria to low, but not high, pH. Growth inhibition of these organisms at both extremes of pH was associated with enhanced loss of K⁺ from pressurized cells. Inhibited cells in alkaline media also lysed under pressure, but microscopically observable lysis was clearly a secondary phenomenon because it occurred slowly. Apparent volumes for growth-inhibitory protonation-deprotonation reactions were calculated on the basis of measured shifts in inhibitory pH with pressure. The values ranged from 99 to 431 ml/mole, and their magnitudes indicated that growth inhibition by acids or bases involves cooperative changes in polymeric interactions such as those which accompany protein denaturation.