Activation and Desensitization of Transducing Pathways by Melvin I. Simon (auth.), T. M. Konijn, M. D. Houslay, P. J.

THR12 point mutation. These cells have a subtle abberant phenotype, forming multiple tips on the developing fruiting bodies (16). Cells also show an enhanced adaptation of the CAMP-stimulated activation of guanylate cyclase (17). Recently it was shown that Ins(1,4,5)P3 levels were increased 3-5 fold in the RAS-THR12 transformants (18). Using a more accurate assay for the determination of [3H]Ins(I,4,5)P3 in [3H]inositol labelled cells by HPLC and of absolute Ins(I,4,5)P3 concentrations by the isotope dilution assay, we reevaluated the 52 inositol cycle in RAS-THR12 transformed cells.

Exhaustion of the food ;: f "t" UNICELLULAR \ r~~:~~ture GROWTH source induces a developmental program: cells aggregate by means ,,~"fo0 , of a chemotactic reaction to a MULTICELLULAR compound which is secreted by the DIFFERENTIATION starving cells. The aggragate may ~ c=:=:::? /aggregation contain upto 100,000 cells, which are organized in a spatial pattern; pseudoplasmodium about one third of the cell mass at the front differentiate to prestalk cells, while about two third differentiate to prespore cells.

Two serines and 3 threonines are also found in the putative third intracellular 33 loop. Many of the serines have nearby acidic residues which have been implicated in other systems as important receptor kinase recognition sites (Thomson and Findlay, 1984). 5 Figure 6. Localization of Phosphorylatio~ sites to the cterminal domain. Cells were labeled with 3 Pi' with or without cAMP stimulation. Membranes were prepared and resuspended in lysis buffer plus 100 ~g/ml trypsin . After 30 minutes 150 ~g/ml soy bean trypsin inhibitor was added and samples were re-centrifuged.

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