CAK1 promotes meiosis and spore formation in Saccharomyces cerevisiae in a CDC28-independent fashion.
CAK1 encodes a protein kinase in Saccharomyces cerevisiae whose sole essential mitotic role is to activate the Cdc28p cyclin-dependent kinase by phosphorylation of threonine-169 in its activation loop. SMK1 encodes a sporulation-specific mitogen-activated protein (MAP) kinase homolog that is required to regulate the postmeiotic events of spore wall assembly. CAK1 was previously identified as a multicopy suppressor of a weakened smk1 mutant and shown to be required for spore wall assembly. Here we show that Smk1p, like other MAP kinases, is phosphorylated in its activation loop and that Smk1p is not activated in a cak1 missense mutant. Strains harboring a hyperactivated allele of CDC28 that is CAK1 independent and that lacks threonine-169 still require CAK1 to activate Smk1p. The data indicate that Cak1p functions upstream of Smk1p by activating a protein kinase other than Cdc28p. We also found that mutants lacking CAK1 are blocked early in meiotic development, as they show substantial delays in premeiotic DNA synthesis and defects in the expression of sporulation-specific genes, including IME1. The early meiotic role of Cak1p, like the postmeiotic role in the Smk1p pathway, is CDC28 independent. The data indicate that Cak1p activates multiple steps in meiotic development through multiple protein kinase targets.
Schaber
Michael
M
Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Lindgren
Anne
A
Schindler
Karen
K
Bungard
David
D
Kaldis
Philipp
P
Winter
Edward
E
D017489:CDC28 Protein Kinase, S cerevisiae / Q000737:chemistry / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases; D004271:DNA, Fungal / Q000096:biosynthesis; D004789:Enzyme Activation; D000939:Epitopes / Q000737:chemistry / Q000378:metabolism; D005800:Genes, Fungal; D008540:Meiosis / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013172:Spores, Fungal / Q000502:physiology*; D000095043:Cyclin-Dependent Kinase-Activating Kinase
D004271:DNA, Fungal; D000939:Epitopes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D017346:Protein Serine-Threonine Kinases; D017489:CDC28 Protein Kinase, S cerevisiae; D018844:Cyclin-Dependent Kinases; D020928:Mitogen-Activated Protein Kinases; C443670:Smk1 protein, S cerevisiae; D000095043:Cyclin-Dependent Kinase-Activating Kinase