Saccharomyces cerevisiae CDC25(1028-1589) is a guanine nucleotide releasing factor for mammalian Ras proteins and is oncogenic in NIH3T3 cells
1993
Chevallier-Multon, M.C. | Schweighoffer, F. | Barlat, I. | Baudouy, N. | Fath, I. | Duchesne, M. | Tocque, B.
The best characterized yeast guanine nucleotide releasing factor is CDC25, which acts on RAS and thereby stimulates cAMP production in Saccharomyces cerevisiae. In order to determine if CDC25 could be a specific GDP-GTP releasing factor for the mammalian proteins Ha-ras, Ki-ras, and N-ras, its functions were studied both in vitro and in NIH3T3 cells. The 561 amino acids composing the C-terminal domain of CDC25 (CDC25 C-domain) released guanine nucleotides (both GDP and GTP) from Ha-, Ki-, and N-ras but not from Rap1A, Rab5, and Rab11. CDC25 acted on oncogenically activated Ha-ras even if the last 23 amino acids (167-189) of the Ras proteins were not present. CDC25 transformed NIH3T3 cells; its transforming capacity was enhanced by overexpression of wild-type Ha-ras. CDC25 C-domain probably exerts its effects through the activation of cellular Ras proteins. These data suggest that the CDC25 C-domain can function as an upstream activator of Ras proteins in a heterologous system and therefore could be a useful tool to study the regulation of Ras activation by growth factor receptors. class M transcription factor fraction (TFIIIE) from yeast nuclear extracts. TFIIIE is functionally distinct from the standard yeast transcription factor fractions, TFIIIB and TFIIIC. It is also different from either of the TFIIIB subfractions, B' and B''. TFIIIE is essential for specific transcription of both tRNA and 5 S RNA genes, its activity is sensitive to proteinase K, and it exhibits an apparent sedimentation coefficient of 4.0 S when analyzed on glycerol gradients. In the case of a tRNA gene, TFIIIE does not play a role in the formation of stable preinitiation complexes containing TFIIIB and TFIIIC. It is required for single as well as multiple rounds of transcription, however. Thus, TFIIIE is involved in the utilization of stable transcription complexes, but its action is not restricted to reinitiation events.
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