Analysis of Protein Phosphatase-1 and Aurora Protein Kinase Suppressors Reveals New Aspects of Regulatory Protein Function in Saccharomyces cerevisiae

Abstract

Protein phosphatase-1 (PP1) controls many processes in eukaryotic cells. Modulation of mitosis by reversing phosphorylation of proteins phosphorylated by aurora protein kinase is a critical function for PP1. Overexpression of the sole PP1, Glc7, in budding yeast, Saccharomyces cerevisiae, is lethal. This work shows that lethality requires the function of Glc7 regulatory proteins Sds22, Reg2, and phosphorylated Glc8. This finding shows that Glc7 overexpression induced cell death requires a specific subset of the many Glc7-interacting proteins and therefore is likely caused by promiscuous dephosphorylation of a variety of substrates. Additionally, suppression can occur by reducing Glc7 protein levels by high-copy Fpr3 without use of its proline isomerase domain. This divulges a novel function of Fpr3. Most suppressors of GLC7 overexpression also suppress aurora protein kinase, ipl1, temperature-sensitive mutations. However, high-copy mutant SDS22 genes show reciprocal suppression of GLC7 overexpression induced cell death or ipl1 temperature sensitivity. Sds22 binds to many proteins besides Glc7. The N-terminal 25 residues of Sds22 are sufficient to bind, directly or indirectly, to seven proteins studied here including the spindle assembly checkpoint protein, Bub3. These data demonstrate that Sds22 organizes several proteins in addition to Glc7 to perform functions that counteract Ipl1 activity or lead to hyper Glc7 induced cell death. These data also emphasize that Sds22 targets Glc7 to nuclear locations distinct from Ipl1 substrates.

Histone Chaperone Paralogs Have Redundant, Cooperative, and Divergent Functions in Yeast

“…The genetic interactions annotated here support a unique function for Fpr3 in orchestrating centromeric chromatin dynamics during chromosome segregation. This is fully consistent with existing literature (Hochwagen et al 2005; Krogan et al 2006; Macqueen and Roeder 2009; Ghosh and Cannon 2013; Ohkuni et al 2014). Our comparative analysis provides additional systems-level evidence that this role is not shared with Fpr4, indicating that Fpr3, potentially as a homo-oligomer, may regulate chromatin in a way that affects chromosome segregation (Hochwagen et al 2005; Macqueen and Roeder 2009).…”

The Hsp70 homolog Ssb and the 14-3-3 protein Bmh1 jointly regulate transcription of glucose repressed genes inSaccharomyces cerevisiae

“…Most relevant in the context of this study, five of the identified Ssb-interactors comprise the central components of the SNF1/Glc7 signaling pathway: Snf1, Sip1 and Snf4, which form a holo-SNF1 complex, Glc7 and Reg1 (Table 1 and Figure 3D ) ( 2 , 3 ). Ssb also formed a crosslink to Sds22, an essential, however poorly characterized subunit of Glc7 ( 49 ), which also contacts Snf4 ( 50 ) and is phosphorylated by SNF1 (Yeast Kinase Interaction Database, 51 ). Employing a cleavable crosslinker, the interaction between Snf1 and Ssb was confirmed via immunoblotting (Figure 3C ).…”

The N-Terminal Region of Yeast Protein Phosphatase Ppz1 Is a Determinant for Its Toxicity

“…Similarly to Ppz1, the overexpression of Glc7 has been revealed to be deleterious for the cell [ 34 , 35 ]. However, a number of evidences suggest that the mechanisms for toxicity are not the same [see [ 28 ] for a discussion].…”