Mutation in continuous cultures of Schizosaccharomyces Pombe. I. Dependence of the kinetics of mutation accumulation upon the growth-limiting nutrilite

The rate of spontaneous mutation to resistance to the 12,13-epoxytrichothecene trichodermin has been determined under different growth limiting conditions in continuous cultures of the microbial eukaryote Schizosaccharomyces pombe. In agreement with data obtained in bacterial systems by previous workers the kinetics observed for the accumulation of mutations is found to be dependent upon the nutrient used to limit the growth of the population. Under conditions of glucose-limitation mutation accumulation is directly proportional to the rate of cell division, while under histidine-limitation it is proportional to chronological time. Various possible explanations for these observations are discussed.     

Low serum testosterone concentrations in patients with carcinoma of the pancreas

The detection of high activities of two sex-steroid biosynthetic enzymes—aromatase and 5-alpha-reductase—in pancreatic carcinoma tissue suggested the possibility that these enzymes may influence the circulating concentrations of sex-steroid hormones. Mean serum testosterone concentrations in 22 men and women with exocrine carcinoma of the pancreas were significantly lower than those in 20 healthy controls and 27 patients with other known malignancies, who were of similar age and sex composition. Low serum testosterone concentrations may be due to uptake by and metabolism within the tumour; alternatively, patients with low androgen concentrations may be at greater risk of developing pancreatic carcinoma.     

Lipid-linked saccharides formed during pullulan biosynthesis in Aureobasidium pullulans

Radioactive glycolipids were extracted from cells of Aureobasidium pullulanspulsed with d-[¹⁴C]glucose. Labelled, alkali-stable lipids were resolved into one neutral and two acidic fractions. The neutral fraction was stable to mild hydrolysis with acid, whereas the acidic fractions could be hydrolysed, yielding d-glucose and a series of oligosaccharides having mobilities corresponding to those of isomaltose, panose, and isopanose. Amyloglucosidase (EC 3.2.1.3) catalysed the hydrolysis of 60% of the liberated radioactive oligosaccharides to d-glucose, indicating the presence of (1→4)-α- and (1 → 6)-α-d-glucosidic bonds. Since these lipid-linked saccharides are produced during pullulan biosynthesis in A. pullulans, it is proposed that they are intermediates in the biosynthetic pathway of that extracellular polysaccharide. A mechanism incorporating these glycolipids into a possible scheme of polysaccharide assembly is presented.     

Effect of food-deprivation on rat pancreatic islet cells

Somatostatin, insulin and glucagon concentrations in rat pancreas were measured following various intervals of food-deprivation. Tissue concentrations, as measured by radioimmunoassay, were correlated with A-, B-, and D-cell number and size using a scanning integrating image analyzer (Quantimet 720). Alterations in total islet hormone content were not correlated to changes in size or distribution of cells. This implies that changes in tissue content reflect changes in turnover of peptides rather than changes in cell size or number.     

Kinetics of rapid RNA evolution in vitro

Summary A rapidly acquired partial resistance to the replicase antagonist, ethidium bromide (EB), seen by Spiegelman and coresearchers in Q RNA variants competitively replicating under defined conditions in vitro, reflected existence of a pool of mutant RNA molecules, preadapted to EB, and their cross-propagation from the pre-EB optimum species, MDV-1, and from other kindred variants, some of which remained undetected, according to this quantitative analysis of midivariant RNA replication kinetics. DNAlike features of their evolution, such as the cloning of variants from an MDV-1 subtype and a complicance with the fundamental theorem of natural selection, resulted from the suppression, both real and apparent, of intrinsic RNA heterogeneity through sampling and detection methods, and also by the ascendency of self-propagation over cross-propagation with advancement of a superior variant. The deficit in mean polymer fitness, compared with optimum levels, determines the lower limit of this heterogeneity. Stability conditions for frequency equilibrium and strategies for counteracting viral drug resistance have been considered.     

Differential Responses of the Phosphorylation of Ribosomal Protein S6 to Nerve Growth Factor and Epidermal Growth Factor in PC 12 Cells

Previous studies from this laboratory have shown that the phosphorylation of the S6 protein of the ribosomes is catalyzed by at least two different and separable kinase activities in PC12 cells. One of these activities is increased by treatment of the cells with nerve growth factor, the other by treatment of the cells with epidermal growth factor. The present work shows that these two factors stimulate the phosphorylation of S6 with quite different kinetics, and that both the number of phosphates incorporated into S6 and the phosphopeptide pattern of S6 are different in cells treated with nerve growth factor than in cells treated with epidermal growth factor. The characteristics of the nerve growth factor-sensitive S6 kinase and of the epidermal growth factor-sensitive kinase were also clearly different. Substrate specificity and inhibitor studies indicated that neither was identical to cyclic AMP-dependent kinase, kinase C, or the calcium/calmodulin-dependent kinases. However, two major phosphopeptides produced by S6 phosphorylation in nerve growth factor-treated cells were also seen on phosphorylation of S6 by cyclic AMP-dependent kinase in vitro. In addition, when rat liver 40S ribosomal subunits were pretreated with cyclic AMP-dependent kinase in vitro, the action of the nerve growth factor-sensitive S6 kinase was increased about twofold.