A Bub2p-dependent spindle checkpoint pathway regulates the Dbf2p kinase in budding yeast

Abstract

Exit from mitosis in all eukaroytes requires inactivation of the mitotic kinase. This occurs principally by ubiquitin-mediated proteolysis of the cyclin subunit controlled by the anaphase-promoting complex (APC). However, an abnormal spindle and/or unattached kinetochores activates a conserved spindle checkpoint that blocks APC function. This leads to high mitotic kinase activity and prevents mitotic exit. DBF2 belongs to a group of budding yeast cell cycle genes that when mutated prevent cyclin degradation and block exit from mitosis. DBF2 encodes a protein kinase which is cell cycle regulated, peaking in metaphase-anaphase B/telophase, but its function remains unknown. Here, we show the Dbf2p kinase activity to be a target of the spindle checkpoint. It is controlled specifically by Bub2p, one of the checkpoint components that is conserved in fission yeast and higher eukaroytic cells. Significantly, in budding yeast, Bub2p shows few genetic or biochemical interactions with other members of the spindle checkpoint. Our data now point to the protein kinase Mps1p triggering a new parallel branch of the spindle checkpoint in which Bub2p blocks Dbf2p function.

The Role of the Polo Kinase Cdc5 in Controlling Cdc14 Localization

“…Previous studies suggested that Cdc5 activated the MEN kinase Dbf2 in a BUB2-independent manner (Fesquet et al, 1999, Lee et al, 2001. We, therefore, examined the effects of overexpressing CDC5 and deleting BUB2 on Dbf2 kinase activity.…”

“…Deletion of BUB2 has been shown to cause a slight hyperactivation of the MEN kinase Dbf2 (Fesquet et al, 1999;Lee et al, 2001;Visintin and Amon, 2001). Cells deleted for BUB2 did not release Cdc14 from the nucleolus in a hydroxyurea (HU)-arrest, but inactivation of BUB2 enhanced the ability of CDC5 to promote Cdc14 release from the nucleolus ( Figure 5A).…”

SAC‐ing mitotic errors: How the spindle assembly checkpoint (SAC) plays defense against chromosome mis‐segregation

“…Although it was originally thought that Bub2p functioned in the same pathway as the other Mad and Bub proteins [see Hardwick 1998], it later became clear that Bub2p was unique among the Mads and Bubs in several respects [Alexandru et al, 1999;Fesquet et al, 1999;Fraschini et al, 1999;Li, 1999]. For example, budding yeast Bub2p localizes to spindle pole bodies but not to kinetochores [Fraschini et al, 1999], and degradation of Pds1p by the 26S proteasome is delayed in SACactivated bub2D mutants [Alexandru et al, 1999], indicating that Bub2p, unlike the other Mad and Bub proteins, is not required for SAC inhibition of APC/CCdc20p mediated protein degradation [reviewed in Taylor, 1999].…”

“…of budding yeast Mps1p fails to activate the spindle checkpoint in the absence of Mad3p, Bub1p, Bub2p, or Bub3p [Hardwick et al, 1996], budding yeast Mps1p regulates Dbf2p, a protein involved in the mitotic exit branch of the SAC [Fesquet et al, 1999], and fission yeast mph1 acts upstream of cdc16 and dma1 (S. Kadura and S. Sazer, unpublished data).…”

Human MPS1 Kinase Is Required for Mitotic Arrest Induced by the Loss of CENP-E from Kinetochores

“…MPS1, BUB1, BUB3, MAD1, MAD2, and MAD3 monitor kinetochore microtubule attachments and prevent premature chromosome segregation by inhibiting degradation of securin/Pds1 and mitotic cyclins (Wassmann and Benezra, 2001;Peters, 2002). BUB2 acts along a different pathway that monitors spindle integrity and orientation and prevents premature cytokinesis by inhibiting the degradation of the mitotic cyclin Clb2 (Alexandru et al, 1999;Fesquet et al, 1999;Fraschini et al, 1999;Li, 1999;Bardin et al, 2000;Bloecher et al, 2000;Pereira et al, 2000).Many of the mitotic checkpoint genes in yeast are evolutionarily conserved, because orthologues of MAD1, MAD2, MAD3, BUB1, and BUB3 have been identified in worms, flies, and mammals (Chen et al, 1996;Li and Benezra, 1996;Taylor and McKeon, 1997;Basu et al, 1998;Cahill et al, 1998;Chan et al, 1998;Gorbsky et al, 1998;Jablonski et al, 1998;Jin et al, 1998;Taylor et al, 1998;Basu et al, 1999;Kitagawa and Hieter, 2001). Importantly, many of these mitotic checkpoint proteins bind preferentially to unattached kinetochores, where they are postulated to function in generating the "wait anaphase signal" (Hoffman et al, 2001, and references therein).…”