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Publisher Summary This chapter describes the Ras and Rap I interaction with AF-6 effector target. The chapter presents a spectrum of investigative approaches that served to demonstrate specific protein interactions among the Ras/Rapl GTPases and their potential effector molecule AF-6 in vivo and in vitro . The Rap types of small GTPases are members of the Ras superfamily and are the molecules that show the most identity with the oncogenic Ras proteins. Whereas the interaction of activated Ras proteins with their downstream effectors Raf, Ral guanine nucleotide dissociation stimulator (RalGDS), and phosphatidylinositol 3-kinase (PI3K) leads to a fairly defined picture, the role of Rapl is as yet poorly understood. The two-hybrid analysis and the investigation of the kinetic and thermodynamic properties of Ras-AF-6 and Rapl-AF-6 complexes leads to the same overall outcome—namely, Rap1 appears to form the tightest complex with AF-6-RBD1. The chapter concludes with a discussion on methods to quantitate Ras/Rapl and AF-6 interactions.

Cells of the yeast Saccharomyces cerevisiae display a wide range of glucose‐induced regulatory phenomena, including glucose‐induced activation of the RAS‐adenylate cyclase pathway and phosphatidylinositol turnover, rapid post‐translational effects on the activity of different enzymes as well as long‐term effects at the transcriptional level. A gene called GGS1 (for General Glucose Sensor) that is apparently required for the glucose‐induced regulatory effects and several ggs1 alleles (fdp1, byp1 and cif1) has been cloned and characterized. A GGS1 homologue is present in Methanobacterium thermoautotrophicum. Yeast ggs1 mutants are unable to grow on glucose or related readily fermentable sugars, apparently owing to unrestricted influx of sugar into glycolysis, resulting in its rapid deregulation. Levels of intracellular free glucose and metabolites measured over a period of a few minutes after addition of glucose to cells of a ggsi1Δ strain are consistent with our previous suggestion of a functional interaction between a sugar transporter, a sugar kinase and the GGS1 gene product. Such a glucose‐sensing system might both restrict the influx of glucose and activate several signal transduction pathways, leading to the wide range of glucose‐induced regulatory phenomena. Deregulation of these pathways in ggs1 mutants might explain phenotypic defects observed in the absence of glucose, e.g. the inability of ggs1 diploids to sporulate. Copyright © 1993, Wiley Blackwell. All rights reserved