Abstract:
:Recently, we described the constitutive activation of Mek1 by mutation of its two serine phosphorylation sites. We have now characterized the biochemical properties of these Mek1 mutants and performed microinjection experiments to investigate the effect of an activated Mek on oocyte maturation. Single acidic substitution of either serine 218 or 222 activated Mek1 by 10-50 fold. The double acidic substitutions, [Asp218, Asp222] and [Asp218, Glu222], activated Mek1 over 6000-fold. The specific activity of the [Asp218, Asp222] and [Asp218, Glu222] Mek1 mutants, 29 nanomole phosphate per minute per milligram, is similar to that of wild-type Mek1 activated by Raf-1 in vitro. Although the mutants with double acidic substitutions could not be further activated by Raf-1, three of those with single acidic substitution were activated by Raf-1 to the specific activity of activated wild-type Mek1. Injection of the [Asp218, Asp222] Mek1 mutant into Xenopus oocytes activated both MAP kinase and histone H1 kinase and induced germinal vesicle breakdown, an effect that was only partially blocked by inhibition of protein synthesis. These data provide a measure of Mek's potential to influence cell functions and a quantitative basis to assess the biological effects of Mek1 mutants in a variety of circumstances.
journal_name
Mol Biol Celljournal_title
Molecular biology of the cellauthors
Huang W,Kessler DS,Erikson RLdoi
10.1091/mbc.6.3.237subject
Has Abstractpub_date
1995-03-01 00:00:00pages
237-45issue
3eissn
1059-1524issn
1939-4586journal_volume
6pub_type
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