The Ama1-Directed Anaphase-Promoting Complex Regulates the Smk1 Mitogen-Activated Protein Kinase During Meiosis in Yeast

Abstract

Smk1 is a meiosis-specific MAPK homolog in Saccharomyces cerevisiae that regulates the postmeiotic program of spore formation. Similar to other MAPKs, it is activated via phosphorylation of the T-X-Y motif in its regulatory loop, but the signals controlling Smk1 activation have not been defined. Here we show that Ama1, a meiosis-specific activator of the anaphase-promoting complex/cyclosome (APC/C), promotes Smk1 activation during meiosis. A weakened allele of CDC28 suppresses the sporulation defect of an ama1 null strain and increases the activation state of Smk1. The function of Ama1 in regulating Smk1 is independent of the FEAR network, which promotes exit from mitosis and exit from meiosis I through the Cdc14 phosphatase. The data indicate that Cdc28 and Ama1 function in a pathway to trigger Smk1-dependent steps in spore morphogenesis. We propose that this novel mechanism for controlling MAPK activation plays a role in coupling the completion of meiosis II to gamete formation.

Sporulation in the Budding Yeast Saccharomyces cerevisiae

“…Addtionally, mutations in the APC subunit Swm1 cause a spore wall defect similar to smk1D mutants (Ufano et al 1999;Hall et al 2003). This may reflect the requirement for the APC activator Ama1 for Smk1 activation (McDonald et al 2005).…”

“…S. Park, personal communication). Additionally, AMA1 is required for the activation of the Smk1 kinase that regulates spore wall assembly (McDonald et al 2005). Again, this effect on activation is independent of Ssp1 degradation (E. Winter, personal communication).…”

The Ras/cAMP Pathway and the CDK-Like Kinase Ime2 Regulate the MAPK Smk1 and Spore Morphogenesis in Saccharomyces cerevisiae

“…The mnd2-D strain was also spo11-D to prevent checkpoint-mediated arrest due to the unregulated activation of Ama1. The phosphorylated (active) form of Smk1-HA is indicated with a circled P. positively regulates Smk1 activation (McDonald et al 2005). Mnd2 is a subunit of the APC that specifically inhibits Ama1 (Oelschlaegel et al 2005;Penkner et al 2005).…”

“…Instead, Smk1 is activated through T-loop phosphorylation by Cak1 similar to Ime2 (Wagner et al 1997;Schaber et al 2002). Positive regulators of Smk1 activation include Ama1 (McDonald et al 2005), a meiosis-specific Cdc20-family member that links substrates to the APC (Cooper et al 2000). It has been proposed that the APC Ama1 plays a role in coupling completion of the meiotic divisions to gamete formation (Oelschlaegel et al 2005;Penkner et al 2005).…”

“…It has been proposed that the APC Ama1 plays a role in coupling completion of the meiotic divisions to gamete formation (Oelschlaegel et al 2005;Penkner et al 2005). Ssp2, a middle meiosis-specific protein that regulates spore formation (Sarkar et al 2002;Coluccio et al 2004;Li et al 2007) is also required for efficient phosphorylation of Smk1's activation loop (McDonald et al 2005). Thus, while Smk1 is a MAPK family member on the basis of its sequence and its activation by T-loop phosphorylation, it is unlike other MAPKs in several key respects; it is tightly controlled at the transcriptional level, it is activated by a CDK activating kinase, it is regulated by the APC, and its activation state is largely controlled by internally generated signals rather than extracellular ligands.…”