A protein factor for ras p21-dependent activation of mitogen-activated protein (MAP) kinase through MAP kinase kinase

T. Itoh, K. Kaibuchi, T. Masuda, T. Yamamoto, Y. Matsuura, A. Maeda, K. Shimizu, Y. Takai

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50 Citations (Scopus)

Abstract

To identify the direct target molecule of ras p21 in higher eukaryotes, we have recently developed the cell-free system in which ras p21 activates mitogen-activated protein (MAP) kinase/extracellular signal-regulated kinase (ERK). In this cell-free system, the guanosine 5'-[γ-thio]triphosphate- bound form of Ki-ras p21, but not the GDP-bound form, activates endogenous Xenopus MAP kinase as well as recombinant ERK2 in the presence of the cytosol fraction of Xenopus oocytes. We separated two protein factors from the cytosol fraction of Xenopus oocytes by column chromatography: one was the inactive form of MAP kinase kinase and the other was a factor tentatively named ras p21-dependent ERK-kinase stimulator (REKS). The former and latter showed M(r) values of ≃45,000 and 150,000-200,000, respectively, as estimated by gel filtration. Both factors were necessary for Ki-ras p21- dependent activation of MAP kinase/ERK2. These results indicate that an additional protein factor (REKS) is essential for Ki-ras p21 to activate MAP kinase through MAP kinase kinase.

Original languageEnglish
Pages (from-to)975-979
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume90
Issue number3
DOIs
Publication statusPublished - 1993
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General

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