Effect of 5,7-unsaturated sterols on ethanol tolerance in Saccharomyces cerevisiae.

Structural membrane lipids are known to contribute to the high ethanol resistance of Saccharomyces cerevisiae (2, 4, 17). By manipulating the yeast cellular sterol level by changing the carbon-to-nitrogen source ratio in the chemostat growth medium, high delta 5,7-sterol levels were found to increase the resistance of yeast populations to ethanol-induced death. The resistance of the erg2 (delta 8----delta 7-sterol isomerase) mutant to ethanol-induced death was generally comparable with that of the delta 5,7-sterol-synthesizing strain. In contrast, the sensitivity of anaerobic growth to inhibition by ethanol was higher in the erg2 mutant in comparison with the delta 5,7-sterol-synthesizing strains but a high level of those sterols increased the vulnerability of anaerobic growth to ethanol inhibition.     

Cutting edge: precursor frequency affects the helper dependence of cytotoxic T cells.

Generation of CTL immunity often depends on the availability of CD4 T cell help. In this report, we show that CTL responses induced by cross-priming can be converted from CD4-dependent to CD4-independent by increasing the frequency of CTL precursors. In the absence of CD4 T cells, high numbers of CTL precursors were able to expand in number and become effector CTL. The ability of high frequencies of CD8 T cells to override help was not due to their ability to signal CD40 via expression of CD154. These findings suggest that when precursor frequencies are high, priming of CD8 T cell responses may not require CD4 T cell help.     

Isolation of pleiotropic yeast mutants requiring ergosterol for growth

Mutant strains of Saccharomyces cerevisiae which require ergosterol for growth have been isolated. These mutants are all petite and require a fatty acid. Several mutants require methionine in addition. These mutants have been classified into 6 complementation groups. For one of the mutants the enzymatic block has been localized after lanosterol. These mutants do not show a stringent requirement for ergosterol, as sitosterol, stigmasterol or cholesterol also support growth. Mutants of this type will be of value not only in studies of sterol biosynthesis, but also in assessing the biological role of sterols in the cytoplasmic yeast membrane. Similar mutants but without a stringent requirement for a sterol have been previously isolated by Resnick and Mortimer (8).     

Ultrastructure of the Flame Bulbs of Urastoma cyprinae (Platyhelminthes, ‘Prolecithophora’, Urastomidae)

The ultrastructure of the flame bulbs of the turbellarian Urastoma cyprinae from Mytilus galloprovincialis in the Mediterranean is described. The nucleus of the terminal cell is located some distance basal to the rootlets of the cilia forming the flame; the cytoplasm contains numerous tubules approximately 54–66 nm in diameter, and vesicles. Thick walled, densely packed rod-like structures coil around each other with a tendency towards longitudinal orientation close to the flame. The rod-like structures tightly surround the basal part of the flame and the distal cytoplasmic tube in the apical part of the flame. Some of them, including the inner predominantly longitudinally directed ones, are continuous with the cytoplasm of the terminal cell, others are continuous with the cytoplasm of the distal cytoplasmic tube. Internal leptotriches arise from the cytoplasm of the terminal cell and intrude between the basal parts of the cilia of the flame. The distal cytoplasmic tube possesses a septate junction. The flame bulb of Urastoma differs distinctly from those known from other Platyhelminthes; implications for the phylogeny of Platyhelminthes are discussed.     

Renin cleavage of a human kidney renin substrate analogous to human angiotensinogen, H-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Ser-OH, that is human renin specific and is resistant to cathepsin D

A synthetic tetradecapeptide, H-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Ser-OH, which corresponds to the 13 amino terminal residues of human angiotensinogen plus a carboxy terminal serine to replace a suggested site of carbohydrate attachment, has been shown to be a good substrate for human kidney renin. At pH 7.2 and 37 degrees C the KM or Michaelis constant was 8.4 +/- 2.9 microM, and the VM or velocity at infinite tetradecapeptide concentration was 11.3 +/- 2.4 mumol angiotensin I made per hour per milligram renin. The tetradecapeptide was highly resistant to cleavage by mouse submaxillary renin. The tetradecapeptide was also slowly cleaved by human liver cathepsin D, by rabbit lung angiotensin-converting enzyme, and by reconstituted human serum, but did not yield angiotensin I. Thus, this synthetic renin substrate should permit more specific measurement of human kidney renin activity.     

A cladistic analysis of the genera in the subfamily Pudicinae (Nematoda, Trichostrongyloidea, Heligmonellidae).

A parsimony analysis was performed on 37 specific taxa belonging to the subfamily Pudicinae (family Heligmonellidae), which contains parasites mainly from South American caviomorph rodents. Thirteen characters were used from the synlophe (rotation of axis, presence of carene, carene asymmetry, presence of comaretes, single ventral comarete length, ridge discontinuity, ventral ridge numbers, presence of a peculiar posterior synlophe, presence of supernumerary spines) and the male caudal bursa (relative length of rays 9 and 10, caudal bursa type, division of the dorsal ray, divergence of the 10th rays). The cladogram shows a consistency index of 1.0. The subfamily Pudicinae has two synapomorphies. Two suprageneric groups are recognized. Suprageneric group 1 shows one synapomorphy and contains Heligmostrongylus, Fuellebornema, Sciurodendrium and Pseudoheligmosomum; suprageneric group 2 shows two synapomorphies and contains Pudica, Acanthostrongylus, Justinema and Durettestrongylus. Five genera are defined on the basis of synapomorphies. The genera Heligmostrongylus, Sciurodendrium and Pudica which are considered paraphyletic, however, are retained due to lack of knowledge as to their relationships.     

Dihydrofolate reductase from a methotrexate-resistant Escherichia coli: Proton magnetic resonance studies of complexes with folate and methotrexate

Proton magnetic resonance studies of 1:1 complexes of E. coli dihydrofolate reductase with folate and methotrexate were performed. A resonance at 1850 Hz in 1:1 enzyme-folate was assigned as the C-7 proton of bound folate by comparison with the spectra of enzyme complexed with folate specifically deuterated at C-7. The first order rate constant for folate dissociation was calculated to be less than 110 sec^?1. Four of the five histidine residues exhibited the same pK's and chemical shifts in the two complexes with pK values of 8.0, 7.3, 6.5 and ～5. However, one histidine increased its pK by 0.7 units (6.25→6.95) and its C-2 proton resonance shifted upfield 50 Hz when folate was substituted for methotrexate. Comparison of these results with those of chemical modification and ultraviolet difference spectroscopy experiments suggests that this histidine may be in the folate binding site — possibly near the pteridine portion of that site.     

The Role of Microsite Conditions in Restoring Trembling Aspen (Populus tremuloides Michx) from Seed

Encouraging natural regeneration of Populus tremuloides Michx (trembling aspen) from seed is a largely unexplored means for reintroducing the species into reclamation areas. We evaluated the effects of microsite (surface contour and substrate type) on aspen seedling establishment and growth on a reclaimed coal mine. The 4.6 ha study site was divided into six 48 m‐wide strips that had 15 or 40 cm capping material salvaged from a nearby forest floor added to the mine surface. We surveyed 126 m long transects located in the center of each strip for microsite conditions, and the presence and height of aspen seedlings. We found that aspen seedlings generally preferred mineral‐organic substrates and concave microsites. To facilitate the regeneration of aspen by seed, we suggest that land managers increase small‐scale roughness and microtopographic diversity on reclaimed sites .