Biomedical subjects

Benjamin A Wolfe

Publications and source records attributed to Benjamin A Wolfe.

5 recordsLinked to original sources

PubMed2006

Phospho-regulation of the Cdc14/Clp1 phosphatase delays late mitotic events in S. pombe.

In eukaryotes, exit from mitosis occurs through the inactivation of the Cdk1-cyclin B kinase complex and the reversal of its phosphorylation events. These late mitotic events are tightly regulated to occur only after the onset of anaphase and prior to cytokinesis. Central to this regulation is the conserved Cdc14 family of protein phosphatases, whose activity reverses Cdk-dependent phosphorylation events. S. cerevisiae Cdc14 activity is restrained from dephosphorylating Cdk substrates and inactivating Cdk1 through its nucleolar sequestration prior to anaphase. Here, we describe a unique mode of Cdc14 regulation that operates prior to anaphase in fission yeast. Cdk1 phosphorylates and inhibits the catalytic activity of the Cdc14 family member, Clp1/Flp1. As Cdk1 activity declines during anaphase progression, Clp1/Flp1 autocatalytically reverses these phosphorylation events to stimulate its own activity. These findings point to a simple regulatory circuit that couples Cdk1 activation with its inactivation mediated through phosphorylation-dependent regulation of Clp1/Flp1 phosphatase activity.

CDC2 Protein Kinase↗

PubMed2005

Split decisions: coordinating cytokinesis in yeast.

Cytokinesis in eukaryotes involves the regulated assembly and contraction of a ring comprising filamentous (F)-actin and myosin II. Assembly of the contractile ring occurs through the accumulation of cortical cues at the specified division plane, followed by recruitment of F-actin, myosin II and accessory proteins involved in generating the mature ring. Ring contraction is temporally regulated to occur only after chromosome segregation and, in yeast, it is controlled by a conserved signaling cascade that becomes active only after Cdk1-Cyclin-B inactivation. In this article (which is part of the Cytokinesis series), we discuss recent studies that have begun to clarify both the spatial and the temporal order of ring assembly and that have illuminated the signals that trigger ring contraction in yeast. These studies add to the growing knowledge of the processes that control eukaryotic cell division.

Cell Division↗

PubMed2004

Inactivating Cdc25, mitotic style.

Mitotic entry and exit require activation and inactivation of the Cdk1-cyclin B kinase complex, respectively. The Cdc25 protein phosphatase family activates Cdk1-cyclin B at the G2/M transition by removing inhibitory phosphate groups. Cdc25 family members, held inactive during interphase, are activated during mitotic progression in an amplification loop involving Cdk1-cyclin B. While Cdc25 activation at the G2/M transition is required for the timely initiation of mitosis, recent evidence suggests that the inactivation of Cdc25 in late mitosis may play a role in supporting Cdk1-cyclin B inactivation. Here, we discuss the mechanisms of Cdc25 regulation and how they pertain to both mitotic entry and exit.

Animals↗

PubMed2004

Fission yeast Clp1p phosphatase affects G2/M transition and mitotic exit through Cdc25p inactivation.

The Cdc14 family of phosphatases specifically reverses proline-directed phosphorylation events. In Saccharomyces cerevisiae, Cdc14p promotes Cdk1p inactivation at mitotic exit by reversing Cdk1p-dependent phosphorylations. Cdk1p is a proline-directed kinase whose activity is required in all eukaryotes for the transit into mitosis. At mitotic commitment, Cdk1p participates in its own regulation by activating the mitotic inducing phosphatase, Cdc25p, and inhibiting the opposing kinase, Wee1p. We have investigated the ability of Schizosaccharomyces pombe Clp1p, a Cdc14p homolog, to disrupt this auto-amplification loop. We show here that Clp1p is required to dephosphorylate, destabilize, and inactivate Cdc25p at the end of mitosis. Clp1p promotes recognition of Cdc25p by the anaphase-promoting complex/cyclosome, an E3 ubiquitin ligase. Failure to inactivate and destabilize Cdc25p in late mitosis delays progression through anaphase, interferes with septation initiation network signaling, and additionally advances the commitment to mitotic entry in the next cycle. This may be a widely conserved mechanism whereby Cdc14 proteins contribute to Cdk1p inactivation.

CDC2 Protein Kinase↗

PubMed2002

Proteomics analysis identifies new components of the fission and budding yeast anaphase-promoting complexes.

The anaphase-promoting complex (APC) is a conserved multisubunit ubiquitin ligase required for the degradation of key cell cycle regulators. Components of the APC have been identified through genetic screens in both Schizosaccharomyces pombe and Saccharomyces cerevisiae as well as through biochemical purification coupled with mass spectrometric protein identification. With these approaches, 11 subunits of the core S. cerevisiae APC have been identified. Here, we have applied a tandem affinity purification approach coupled with direct analysis of the purified complexes by mass spectrometry (DALPC) to reveal additional subunits of both the S. pombe and S. cerevisiae APCs. Our data increase the total number of identified APC subunits to 13 in both yeasts and indicate that previous approaches were biased against the identification of small subunits. These results underscore the power of direct analysis of protein complexes by mass spectrometry and set the foundation for further functional and structural studies of the APC.

Anaphase↗