v-Src induces elevated levels of diglyceride by stimulation of phosphatidylcholine hydrolysis.

When Rat-1 cells bearing the ts LA29 mutant of Rous sarcoma virus (Rat1 LA29) are shifted from restrictive to permissive temperature, the pp60v-Src tyrosine kinase is activated and there is an increase in the cellular level of sn1,2-diacylglycerol (DRG) within 30 min which is not accompanied by increased inositol phospholipid hydrolysis. Temperature shift also increases the hydrolysis of phosphatidylcholine (PC), as determined by an increase in the generation of water soluble choline metabolites. Transphosphatidylation studies have shown that this occurs at least in part via a phospholipase D (PLD) catalysed pathway.     

Anti-adenovirus type 5 cytotoxic T lymphocytes: immunodominant epitopes are encoded by the E1A gene.

Virus specific, major histocompatibility complex-restricted, cytotoxic T lymphocytes (CTL) generated in Fischer strain rats infected with human adenovirus type 5 (Ad5) were found to recognize antigenic determinants encoded within the Ad5 early region 1A (E1A) gene. Preliminary mapping studies suggest that the E1A CTL epitopes are encoded within the regions between bp 625 to 810 and 916 to 974 in the first exon of this gene. These epitope-coding regions occur within subregions of E1A that are conserved functionally, and to some extent structurally (approximately 50% sequence homology), among adenoviruses of different groups. Nevertheless, Ad5-specific CTL lysed only targets infected with adenoviruses of the same group (group C; e.g., Ad2) and not targets infected with adenoviruses of different groups (groups A, B, and E). These results suggest that virus-specific CTL may limit adenoviral dissemination by destroying virus-infected cells at an early stage in the viral replicative cycle, during E1A gene expression. Expression of other adenovirus genes does not appear to be required to target infected cells for elimination by CTL.     

Seasonal carbon isotope discrimination in a grassland community

Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.     

Sensitization of low-dose-rate irradiation by nonlethal hyperthermia

To assess whether hyperthermia could radiosensitize cells irradiated at a low dose rate, Chinese hamster V79 cells were simultaneously heated and irradiated at 0.86 Gy/h. The data showed that heat treatments at 39 and 40 degrees C, which did not induce heat killing alone or high-dose-rate radiosensitization, resulted in enhanced cell killing with low-dose-rate irradiation. The dose-modification factor (ratio of the slopes of the curves for low dose rate and high dose rate) was reduced to 1.8 at 39 degrees C and 1.4 at 40 degrees C, compared to a value of 2.1 at 37 degrees C. These data indicate that nonlethal heat treatments can cause enhanced radiosensitization under low-dose-rate conditions. The implications of these results for interstitial thermoradiotherapy are discussed.     

Suppression of hepatic prostaglandin F2 alpha in rats by dietary alpha-tocopherol acetate is independent of total hepatic alpha-tocopherol.

Groups of eight weanling female F344/N rats were fed semipurified diets that supplied 0, 50, 500, 5000, or 15,000 mg alpha-tocopherol acetate/kg diet, with and without 0.05% phenobarbital (PB) for 9 weeks. Both plasma and hepatic alpha-tocopherol levels, measured by HPLC, strongly correlated with alpha-tocopherol intake (r greater than 0.73, p less than 0.0001). Phenobarbital both depleted hepatic alpha-tocopherol and increased plasma alpha-tocopherol significantly. Although treatment with PB for 9 weeks significantly increased GST activity, PB did not affect hepatic prostaglandin (PG)F2 alpha status, as determined by radioimmunoassay. PGF2 alpha was significantly greater (by 52%) in rats fed no alpha-tocopherol than in rats fed 15,000 mg alpha-tocopherol acetate/kg diet. Hepatic PGF2 alpha status was correlated inversely but weakly with dietary alpha-tocopherol (r = -0.24, p less than 0.05). Hepatic PGF2 alpha status was not correlated with hepatic or plasma alpha-tocopherol status. This finding suggests either that there is a small depletion-resistant subcellular alpha-tocopherol pool which regulates PGF2 alpha production or that alpha-tocopherol alters PGF2 alpha production in vivo by an indirect mechanism.     

Fungal growth during rice tapé fermentation

Fungal growth was quantified during Indonesian rice tapé fermentation using an agar-film technique following sample homogenization for 1 min at 25000 rev/min. After 72 h fermentation, mould hyphal length was 0·68 km/g, yeast hyphal length 2·1 km/g and the numbers of mould chlamydospores and single yeast cells were 14 times 10⁵/g and 5·1 times 10⁷/g respectively. The estimated fungal biomass in rice tapé after 72 h was 25 mg/g dry weight with 62% of this being mould hyphae, 24% mould chlamydospores, 13% yeast hyphae and 1% yeast cells.     

Tumor suppressor p53: analysis of wild-type and mutant p53 complexes.

It has been suggested that the dominant effect of mutant p53 on tumor progression may reflect the mutant protein binding to wild-type p53, with inactivation of suppressor function. To date, evidence for wild-type/mutant p53 complexes involves p53 from different species. To investigate wild-type/mutant p53 complexes in relation to natural tumor progression, we sought to identify intraspecific complexes, using murine p53. The mutant phenotype p53-246(0) was used because this phenotype is immunologically distinct from wild-type p53-246+ and thus permits immunological analysis for wild-type/mutant p53 complexes. The p53 proteins were derived from genetically defined p53 cDNAs expressed in vitro and also from phenotypic variants of p53 expressed in vivo. We found that the mutant p53 phenotype was able to form a complex with the wild type when the two p53 variants were cotranslated. When mixed in their native states (after translation), the wild-type and mutant p53 proteins did not exhibit any binding affinity for each other in vitro. Under identical conditions, complexes of wild-type human and murine p53 proteins were formed. For murine p53, both the wild-type and mutant p53 proteins formed high-molecular-weight complexes when translated in vitro. This oligomerization appeared to involve the carboxyl terminus, since truncated p53 (amino acids 1 to 343) did not form complexes. We suggest that the ability of the mutant p53 phenotype to complex with wild type during cotranslation may contribute to the transforming function of activated mutants of p53 in vivo.     

Aromaticity at position 37 in human epidermal growth factor is not obligatory for activity.

The third disulfide loop (amino acids 33 to 42) of human epidermal growth factor (hEGF) encompasses the region of highest amino acid conservation among all of the EGF-like family of molecules. The importance of some of these highly conserved residues for the maintenance of biological activity, especially the aromatic amino acid tyrosine at position 37, has until now been considered essential on the basis of previous studies with the EGF-like molecule transforming growth factor alpha. Variants at the Tyr-37 position of hEGF were constructed by site-directed mutagenesis. The substituting amino acids were phenylalanine, histidine, serine, alanine, aspartic acid, arginine, and glycine. The variants were tested for their ability to competitively displace native [125I]hEGF from its receptor and to stimulate the protein-tyrosine kinase activity of the receptor; the order of efficacy of substituting amino acids was Phe greater than His greater than Ser greater than Ala greater than Asp greater than Arg greater than Gly in both assays. All were effective, with no or only moderate reduction in potency, in stimulating the incorporation of [3H]thymidine into acid-insoluble material of quiescent mouse A31 cells. Only Tyr-37----Ala, Tyr-37----Arg and Tyr-37----Gly were slightly less potent in the cell assay. Thus, neither tyrosine nor another aromatic amino acid at position 37 in hEGF is essential for full biological activity.