The CD3-gamma and CD3-delta subunits of the T cell antigen receptor can be expressed within distinct functional TCR/CD3 complexes.

The T cell receptor for antigen (TCR) consists of two glycoproteins containing variable regions (TCR-alpha/beta or TCR-gamma/delta) which are expressed on the cell surface in association with at least four invariant proteins (CD3-gamma, -delta, -epsilon and -zeta). CD3-gamma and CD3-delta chains are highly homologous, especially in the cytoplasmic domain. The similarity observed in their genomic organization and their proximity in the chromosome indicate that both genes arose from duplication of a single gene. Here, we provide several lines of evidence which indicate that in human and murine T cells which expressed both the CD3-gamma and CD3-delta chains on their surface, the TCR/CD3 complex consisted of a mixture of alpha beta gamma epsilon zeta and alpha beta delta epsilon zeta complexes rather than a single alpha beta gamma delta epsilon zeta complex. First, a CD3-gamma specific antibody failed to co-immunoprecipitate CD3-delta and conversely, several CD3-delta specific antibodies did not coprecipitate CD3-gamma. Secondly, analysis of a panel of human and murine T cell lines demonstrated that CD3-gamma and CD3-delta were expressed at highly variable ratios on their surface. This suggested that these chains were not expressed as a single complex. Thirdly, CD3-gamma and CD3-delta competed for binding to CD3-epsilon in transfected COS cells, suggesting that CD3-gamma and CD3-delta formed mutually exclusive complexes. The existence of these two forms of TCR/CD3 complexes could have important implications in the understanding of T cell receptor function and its role in T cell development.     

Molecular cloning and expression of the human deoxythymidylate kinase gene in yeast.

(Deoxy)thymidylate (dTMP) kinase is an enzyme which phosphorylates dTMP to dTDP in the presence of ATP and magnesium. This enzyme is important in cellular DNA synthesis because the synthesis of dTTP, either via the de novo pathway or through the exogenous supply of thymidine, requires the activity of this enzyme. It has been suggested that the activities of the enzymes involved in DNA precursor biosynthesis, such as thymidine kinase, thymidylate synthase, thymidylate kinase, and dihydrofolate reductase, are subjected to cell cycle regulation. Here we describe the cloning of a human dTMP kinase cDNA by functional complementation of a yeast dTMP kinase temperature-sensitive mutant at the non-permissive temperature. The nucleotide sequence of the cloned human cDNA is predicted to encode a 24 KD protein that shows considerable homology with the yeast and vaccinia virus dTMP kinase enzymes. The human enzyme activity has been investigated by expressing it in yeast. In this work, we demonstrate that the cloned human cDNA, when expressed in yeast, produces dTMP kinase activity.     

The formation and characteristics of China's existing system

Conclusion To sum up, the character of China's existing system is basically all-embracing totalitarianism formed by the combination of the old tradition of feudal-despotism and the new tradition of Stalinism. This system is the basic source of all the social evils in China.The ultimate aim of the democratic movement is to transform the old, allembracing totalitarian system and to establish a democratic, free, humane, and rational new system. The present ruling group is the beneficiary and defender of the existing system. The contradictions and conflicts between reformers who want to transform the old system and the hardliners who want to protect the old system formed the crux of the struggle of the 1989 democratic movement. Because the democratic movement lacked preparation in theory, organization, tactics and strategy, and because the ruling group controls the means of dictatorship — especially the army —military force was used to suppress the democratic movement with brutal bloodshed. In order to promote the democratic movement, we should sum up some lessons and experiences. First, we should study in depth the existing system and oppose feudaldespotism and Stalinism through effective propaganda and education. Second, we should arouse the democratic consciousness of the broad masses of the people, uniting with them and the healthy elements inside the Party, government, and army to struggle for the smashing of the old system and the establishment of a new system.Su Shaozhi is former Director of the Institute for the Study of Marxism-Leninism and Mao Zedong Thought, Chinese Academy of Social Sciences, Beijing, and currently Visiting Professor at the Bradley Institute for Democracy and Public Values, Marquette University, Milwaukee, Wisconsin     

Lipid composition of liver microsomes in rats fed a high monounsaturated fatty acid diet

The fatty acid and cholesterol contents of tissue membranes are the determinants of membrane stability and functionality. This study was designed to evaluate the influence of a high monounsaturated fatty acid diet on the fatty acid composition of rat liver microsomes and on their cholesterol and lipid phosphorus content. Weanling animals were fed for 5 weeks with high fat diets containing olive oil or corn oil. Saturated fatty acids were increased and oleic acid decreased in microsomal total phospholipids and in the three major phosphoglycerides, phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), of rats fed corn oil as compared to the olive oil group. The percentage of linoleic acid was higher in the corn oil group, but only for total phospholipids and PC. Linoleic and alpha-linolenic metabolites were significantly increased in total phospholipids of olive oil-fed animals with respect to those fed corn oil. These changes were responsible for the low unsaturation index found in microsomal phospholipids of the corn oil group. The diet did not affect the microsome cholesterol or the lipid phosphorus content. These results show that, in olive oil-fed rats, the cholesterol content and the degree of unsaturation of liver microsomes was similar to that observed in weanling animals; this probably suggests an adequate maintenance of functionality of membranes in olive oil-fed animals.     

Effects of microorganisms on effective oxygen diffusion coefficients and solubilities in fermentation media

Effective oxygen diffusion coefficients and solubilities were measured for submerged cultures of Saccharomyces cerevisiae, Escherichia coli, and Penicillium chrysogenum. Both effective oxygen diffusion coefficients and solubilities were found to decrease with increasing cell concentrations in the fermentation media. Comparison of the experimental results of effective oxygen diffusion coefficients in fermentation media with values theoretically predicted on the assumption of unpenetrable microbial cells indicates that oxygen molecules diffuse through the cells during the diffusion process. Within the cell concentration range of typical submerged fermentations, the effective oxygen diffusion coefficient of the fermentation media can be described as D(e) = A(1)f + A(2)f(2). In this equation, fis the cell volume fraction and both A(1) and A(2) are functions of the shape of the cells and the ratio of effective oxygen diffusion coefficient in microbial cells to that in the medium.     

Cytolytic activity of Ia-restricted T cell clones and hybridomas: evidence for a cytolytic mechanism independent of interferon-gamma, lymphotoxin, and tumor necrosis factor-alpha

Ten different helper T cell (Th) hybridomas that are specific to Ia or antigen plus Ia were found to express nonspecific cytolytic activity toward the cytotoxin (CT)-resistant P815 cells upon activation with either Con A or a monoclonal anti-T3 antibody (T3-mAb). In contrast to cytolytic Th1 clones which secrete high levels of interferon-gamma (IFN-gamma) and cytotoxin (CT) (lymphotoxin (LT, also known as TNF-beta) or tumor necrosis factor-alpha (TNF-alpha], these Th hybridomas produce low or undetectable levels of IFN-gamma and CT. No inhibitory activity of IFN-gamma and CT was observed in culture supernatants of activated Th hybridomas. Double-chamber experiments demonstrated that CT-sensitive L929 cells when physically separated from activated Th1 clones were killed by membrane-permeable CT. Under identical experimental conditions, lysis of P815 cells did not occur. Moreover, activation of Th hybridomas directly in wells containing the CT-sensitive L929 cells failed to induce target cell lysis. This confirms that these Th hybridomas produce little CT and argues against high local concentrations of CT being responsible for Th hybridoma-mediated killing of P815 cells. Finally, a polyclonal rabbit antiserum to rTNF-alpha, which strongly and specifically inhibited CT-mediated and Th1 clone-mediated killing of L929 cells, failed to inhibit P815 lysis by activated Th1 clones and Th hybridomas. These observations establish that a cytolytic mechanism independent of IFN-gamma, LT, and TNF-alpha is responsible for lysis of CT-resistant target cells.     

Effect of pertussis toxin on the heart muscarinic-cholinergic receptors and their function

Administration of pertussis toxin to rats induced a significant increase in heart rate that was evident as soon as 24 hours after the administration of the toxin and that persisted for at least 15 days. Electrical stimulation of the vagus decreased dramatically the heart rate of control animals but was unable to do it so in rats treated with pertussis toxin. In cardiac membranes muscarinic agonists decreased adenylate cyclase activity (approximately equal to 20-25%); no effect was observed in membranes obtained from toxin-treated animals. Agonist displacement of antagonist binding [( 3H] Quinuclidinyl benzilate) indicated that treatment with pertussis toxin decreased the proportion of receptors in the high affinity state for agonists. All these data suggest that blockade of the parasympathetic tone plays a key role in the induction of tachycardia by pertussis toxin.     

Starch phosphorylase inhibitor from sweet potato

A protein, starch phosphorylase inhibitor, was purified from the root of sweet potato (Ipomoea batatas [L.] Lam. cv Tainon 65). It had a molecular weight of 250,000 and could be composed of five identical subunits. The isoelectric point of the inhibitor was 4.63. It was a noncompetitive inhibitor toward the sweet potato enzyme with a K_i value of 1.3 × 10⁻⁶ molar when glucose-1-P was the variable substrate. Because cross-reacting materials of rabbit antiphosphorylase inhibitor of sweet potato were found in three arbitrarily selected plant materials, viz. potato tuber, spinach leaf, and rice grain, the occurrence of this protein seemed universal in higher plants. By an immunofluorescence technique, the inhibitor was located in the amyloplast and cell wall where phosphorylase was also found. This implies that they may interact in vivo, and the inhibitor may play an unknown regulatory role against the plant enzyme.     

Substrate specificity of phospholipid/Ca2+-dependent protein kinase as probed with synthetic peptide fragments of the bovine myelin basic protein

The substrate specificity of phospholipid/Ca2+-dependent protein kinase (protein kinase C) was studied using synthetic peptides, in particular those corresponding to the amino acid sequence around serine 115 in bovine myelin basic protein (MBP). It was found that MBP (104-118) and MBP (104-123) were substrates for the enzyme, with apparent Km values of 14 and 10 microM, respectively. Neither MBP (111-118) nor MBP (111-123) were phosphorylated, indicating that an additional segment of sequence extending toward the N terminus, but not toward the C terminus, was essential for the substrate activity of the peptides. Of the alanine-substituted analogs examined, [Ala 105] MBP (104-118) was comparable to the parent peptide, whereas [Ala 107] MBP (104-118) and [Ala 113] MBP-(104-118) were much poorer substrates. These findings indicated that lysine 105 was not essential, but both arginine 107 and arginine 113 were important specificity determinants. Initial studies revealed that [Ala 113] MBP (104-118) inhibited phosphorylation by the enzyme of the parent peptide and, to a lesser extent, the intact MBP(1-170). Serine 115 was the only site phosphorylated in the analog peptides [Ala 105] MBP (104-118) and [Ala 107]MBP (104-118). In the parent peptide, serine 115 was the initial site of phosphorylation but after prolonged phosphorylation other sites became phosphorylated (serine 110 and/or serine 112), further supporting the concept that arginine residues act as essential substrate specificity determinants for phospholipid/Ca2+-dependent protein kinase.     

Stimulation of proliferation ofTetrahymena pyriformis by trace rare earths

Using two Chinese strains ofTetrahymena pyriformis, S1 and BJ4, as the biological models, the effects of lighter rare earths (lanthanum, cerium, praseodymium, neodymium, samarium, and europium), representatives of heavier rare earths (yttrium and thulium), and mixed rare earths were studied. The stimulation of population growth ofTetrahymena in peptone-glucose media containing trace amounts of these elements have been observed. The mechanisms for the beneficial effects of rare earth elements in low concentrations remains to be discovered.