Cak1 Is Required for Kin28 Phosphorylation and Activation In Vivo

Abstract

), we have determined that the KIN28 gene used in two of our experiments ( Fig. 3 and 6) contains two additional mutations that arose during PCR amplification of the sequence from a cDNA library. These mutations result in two amino acid changes in nonconserved regions of the Kin28 protein kinase sequence (N123D and M273T). Since this double mutant gene allows growth of kin28-3 cells and encodes a Kin28 protein with abundant kinase activity ( Fig. 3 and 6), these two mutations do not abolish Kin28 function. However, the presence of these mutations does appear to have an impact on the requirement for T162 phosphorylation in Kin28 function. We showed in Fig. 3 that the T162A mutation blocks Kin28 function, suggesting that phosphorylation at this site might be required for full function. However, G. Faye (unpublished data) and M. Solomon's group (J. Kimmelman, P. Kaldis, C.

The Plant-Specific Kinase CDKF;1 Is Involved in Activating Phosphorylation of Cyclin-Dependent Kinase-Activating Kinases in Arabidopsis

“…Budding yeast Cak1p is known to phosphorylate and activate Kin28p, which is a relative of CDK7-type CAKs in vertebrates (Espinoza et al, 1998;Kimmelman et al, 1999). Therefore, our cak1 ts suppressor assay suggested that CAK1At may also have the activity to phosphorylate CDK7-related CAKs.…”

“…Based on this feature, CAK1At is closely related to Csk1 that exhibits Mcs6-activating kinase activity (Hermand et al, 2001). Cak1p of budding yeast also shows functional similarity to CAK1At as it has the ability to phosphorylate the CDK7-family kinase Kin28p and thereby activate its CTD-kinase activity (Espinoza et al, 1998;Kimmelman et al, 1999). Recently, Tsakraklides and Solomon (2002) reported the comparison of biochemical properties of Csk1, Cak1p, and CAK1At.…”

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

“…Recently, Cak1p kinase that phosphorylates T169 of Cdc28 (Cdk-activating kinase, CAK) was isolated from yeast (Kaldis et al 1996;Thuret et al 1998). However, Pho85p does not appear to be phosphorylated by Cak1p (Espinoza et al 1998), and Pho80-Pho85 function is not affected by cak1-22 mutation (Sutton & Freiman 1997), indicating that Pho85p function is independent of Cak1p. The observation that bacterially produced Pho85p could form a complex with Pcl10p to phosphorylate Gsy2p (W. A.…”

Sporulation in the Budding Yeast Saccharomyces cerevisiae

“…Instead, this activation may involve two essential kinases, Mps1 and Cak1, as hypomorphic forms of each kinase cause spore wall defects reminiscent of smk1D mutants (Wagner et al 1997;Straight et al 2000). Cak1 is known to activate several kinases by phosphorylation of activation loop threonines, and indeed Smk1 is not phosphorylated in the cak1 mutant, and so Cak1 likely functions as a direct activator of Smk1 (Espinoza et al 1996(Espinoza et al , 1998Kaldis et al 1996;Schaber et al 2002;Yao and Prelich 2002;Ostapenko and Solomon 2005). It is not known whether Mps1 directly phosphorylates Smk1.…”