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The Pho85 kinase, a member of the yeast cyclin‐ dependent kinase (Cdk) family, has a regulation mechanism different from Cdks functioning throughout the cell cycle
Author(s) -
Nishizawa Masafumi,
Suzuki Kohji,
Fujino Marie,
Oguchi Tomoko,
Tohe Akio
Publication year - 1999
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1046/j.1365-2443.1999.00290.x
Subject(s) - cyclin dependent kinase , biology , cyclin dependent kinase 1 , cyclin dependent kinase complex , cyclin dependent kinase 2 , microbiology and biotechnology , kinase , cyclin dependent kinase 4 , biochemistry , cell cycle , phosphorylation , cyclin , protein kinase a , cell
Background The PHO85 gene is a negative regulator of the PHO system in the yeast Saccharomyces cerevisiae and encodes a protein kinase (Pho85p) which is highly homologous to the Cdc28 kinase (Cdc28p). Although the two kinases share a 51% identity and their functional domains are well conserved, PHO85 fails to replace CDC28 . Pho85p forms complexes with G 1 ‐cyclin homologues, including Pcl1p, Pcl2p and Pcl9p, and is thought to be involved in the cell‐cycle regulation at G 1 and the end of M. By analysing the genetic and biochemical properties of Pho85p, we studied whether the regulation of Pho85p activity is similar to other cyclin‐dependent kinases (Cdks) directly involved in cell cycle regulation. Results A functional analysis of various Pho85 mutants revealed that E53 in the PSTAIRE sequence was important for Pho85p function. On the other hand, residues in the T‐loop including S166, S167 and E168, appeared dispensable for Pho85p function, suggesting that the phosphorylation of S166, corresponding to T161 of Cdc2p and T169 of Cdc28p, was not required for the kinase activity of Pho85p. Instead, we found that phosphorylation of Y18, corresponding to Y15 of Cdc2p and Y19 of Cdc28p, may be important for the binding of Pho80p but not of Pcl1p, suggesting that tyrosine phosphorylation may function as a signal which discriminates various Pho85‐cyclins. Conclusion In Cdks functioning throughout the cell cycle, tyrosine phosphorylation is inhibitory to the activation of kinase, whereas the phosphorylation of threonine in the T‐loop is essential for activation. Our finding indicates that the regulation mechanism of Pho85p activation appears to be distinct from these Cdks.