Slime moulds

Studies in yeasts (Saccharomyces cerevisiae, Schizo-saccharomyces pombe), slime mould (,Dictyostelium discoideum), worm (Caenorhabditis elegans), fly (Drosophila melanogaster) and mammalian systems have all contributed to our understanding of TOR signalling. 

Slime moulds Badhamia utricularis plasmodia B. utricularis spores Amorphous Spherical Indefinite, extensive 9-12 pm dia... 

H. W. Sauer, K. L. Babcock and H. P. Rusch (1956). High molecular weight phosphorus compound in nucleic acid extracts of the slime mould Physarum polycephalum. J. Bacteriol., 99, 650-661. W. B. Schaefer and C. W. Lewis (1965). Effect of oleic acid on growth and cell structure of Mycobacteria. J. Bacteriol., 90,1438-1446. 

DSrfelt, H., Schmidt, A. R., Ullmann, P. Wunderlich, I. (2003). The oldest fossil myxogastroid slime mould. Mycological Research, 107, 123-6. 

The chemotactic response to cAMP of the slime mould Dictyostelium discoideum is presented as an example. When these cells are starving, they sense cAMP signals, and in response to the hunger signal, cAMP, the cells differentiate (reviewed in ref. 67). In Dictyostelium discoideum the response to cAMP is mediated by G-protein-coupled hepta-helical receptors and is transmitted by the Py subunits of a heterotrimeric G protein. In response to the chemoattractant, cAMP, a homologue of PKB (protein kinase B) is rapidly activated by phosphorylation througji a Ptdins kinase specific for the 3-OH position (see also Chapter 4). 

In the slime mould, Dictyostelium discoideum, a STAT-like DNA-binding protein, DIF (the differentiation-inducing factor), is expressed. DIF is about 700 amino-acid residues long, and has substantial homology with mammalian STATs. DIF is, like STAT, activated by phosphorylation of tyrosines. It is essential for differentiation of the stalk cells of D. discoideum A The long evolutionary path that the STATs have travelled from Dictyostelium to mammals underlines their conserved and essential role as signal transmitters and transcriptional activators in early development. 

Myeophyla (Fnagi) Uyxomyeetes (slime moulds) Mitochondria in Didymium P (60)... 

Two compounds common in plant metabolism are believed to be precursors of isoprenoid cytokinins in plants adenosine-5 -monophosphate (AMP) and A -isopentenylpyrophos-phate (iPP). As a final product of the mevalonate pathway, the latter substance serves also as a precursor for a wide spectrum of metabolites including some other plant hormones, as abscisic acid, gibberellins and brassinosteroids. The hypothetical scheme of reactions resulting in the formation of iPA, Z and DHZ is given in Fig. 2. The enzyme of entry into isoprenoid cytokinin formation is A -isopentenylpyrophosphate 5 -AMP-A -iso-pentenyltransferase (EC 2.5.1.8, trivially named cytokinin synthetase ). This enzyme activity was first detected in a cell-free preparation from the slime mould Dictyostelium discoideum [7,8]. Later the enzyme from higher plants (cytokinin-independent tobacco callus [9,10] and immature Zea mays kernels [11]) was described and the data were recently summarised in [12], The enzyme is very specific as far as the substrate is concerned [13,14] only the nucleotide AMP can be converted and only iPP (with a double bond in A position) may function as a side chain donor. 

The existence of an enzyme activity catalysing cytokinin degradation in plants was first demonstrated in crude homogenates from cultured tobacco cells [103]. Subsequently, the enzyme was characterised in a number of higher plants (reviewed in [104,105]) and named cytokinin oxidase [106]. The presence of cytokinin oxidase activity was also reported in moss protonema [107], cellular slime moulds [108] and yeast [109]. 

In the slime mould Dictyostelium discoideum, a portion of the cellular NDPK has been shown to be plasma membrane-associated. Furthermore Dictyostelium p>ossesses surface cAMP-receptors, which couple to a G-protein, but NDPK activity appears to be activated by the receptor followed by G-protein activation [22]. This activation could be eliminated by the addition of antibodies against NDPK and it was proposed that NDPK was supplying GTP for G-protein activation. 

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