Identification of constitutive and ras-inducible phosphorylation sites of KSR: implications for 14-3-3 binding, mitogen-activated protein kinase binding, and KSR overexpression |
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Authors: | AM Cacace NR Michaud M Therrien K Mathes T Copeland GM Rubin DK Morrison |
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Affiliation: | Program in Molecular Biology, Sloan Kettering Cancer Center and Cornell University Graduate School of Medical Sciences, New York, NY 10021, USA. |
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Abstract: | The chromatin elements targeted by the ATPdependent, Swi-Snf nucleosome-remodeling complex are unknown. To address this question, we generated mutations in yeast histone H2B that suppress phenotypes associated with the absence of Swi-Snf. Sin- (Swi-Snf-independent) mutations occur in residues involved in H2A-H2B dimer formation, dimer- tetramer association, and in the H2B N-terminus. The strongest and most pleiotropic Sin- mutation removed 20 amino acid residues from the H2B N-terminus. This mutation allowed active chromatin to be formed at the SUC2 locus in a snf5Delta mutant and resulted in hyperactivated levels of SUC2 mRNA under inducing conditions. Thus, the H2B N-terminus may be an important target of Swi-Snf in vivo. The GCN5 gene product, the catalytic subunit of several nuclear histone acetytransferase complexes that modify histone N-termini, was also found to act in conjunction with Swi-Snf. The phenotypes of double gcn5Deltasnf5Delta mutants suggest that histone acetylation may play both positive and negative roles in the activity of the Swi-Snf-remodeling factor. |
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