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CASEIN KINASE-II PHOSPHORYLATION INCREASES THE RATE OF SERUM RESPONSE FACTOR-BINDING SITE EXCHANGE

MARAIS, RM; HSUAN, JJ; MCGUIGAN, C; WYNNE, J; TREISMAN, R; (1992) CASEIN KINASE-II PHOSPHORYLATION INCREASES THE RATE OF SERUM RESPONSE FACTOR-BINDING SITE EXCHANGE. EMBO J , 11 (1) 97 - 105.

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Abstract

Recombinant baculoviruses were used to express wild-type serum response factor (SRF) and a mutant, SRF.CKIIA, which lacks all four serine residues in the major casein kinase II (CKII) site at residues 77-90. Purified recombinant SRF binds DNA with an affinity and specificity indistinguishable from that of HeLa cell SRF, and activates transcription in vitro. Comparative phosphopeptide analysis of the wild-type and mutant proteins demonstrated that the wild-type protein is phosphorylated at the major CKII site in insect cells. Dephosphorylation of recombinant SRF does not affect its affinity for the c-fos SRE, and results in only a 3-fold reduction in binding to the synthetic site ACT.L. However, dephosphorylation does cause a large decrease in the rates of association with and dissociation from either site. These effects are due solely to phosphorylation at the major CKII site: the binding properties of the SRF.CKIIA mutant are identical to those of dephosphorylated wild-type SRF, and CKII phosphorylation in vitro converts dephosphorylated wild-type SRF from a slow-binding to a fast-binding form without significantly changing binding affinity. CKII phosphorylation thus acts to potentiate SRF-DNA exchange rates rather than alter equilibrium binding affinity.

Type:Article
Title:CASEIN KINASE-II PHOSPHORYLATION INCREASES THE RATE OF SERUM RESPONSE FACTOR-BINDING SITE EXCHANGE
Keywords:CASEIN KINASE-II, SERUM RESPONSE FACTOR, DNA BINDING, BACULOVIRUS, PHOSPHORYLATION, EPIDERMAL GROWTH-FACTOR, C-FOS ENHANCER, TRANSCRIPTION FACTOR, TERNARY COMPLEX, ELEMENT, PROTEIN, IDENTIFICATION, CELLS, INDUCIBILITY, PURIFICATION

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