Disease relevance of MAD1

• We show that the association between Mad1 and mSin3 is not only dependent on the helical SID but is also dependent on both putative helices of the mSin3 PAH2 region, suggesting that stable interaction requires all three helices [1].

High impact information on MAD1

• Mitotic arrest-deficient (mad) mutants are the subclass of benomyl-sensitive mutants in which the completion of mitosis is not delayed in the presence of benomyl and that die as a consequence of their premature exit from mitosis [2].
• The mad (mitotic arrest-deficient) and bub (budding uninhibited by benzimidazole) mutants of budding yeast lack this checkpoint and fail to arrest the cell cycle when microtubules are depolymerized [3].
• The defect in the top1 trf4-ts mutant is sensed by the MAD1-dependent spindle assembly checkpoint but not by the RAD9-dependent DNA damage checkpoint, further supporting the notion that chromosome structure influences spindle assembly [4].
• Moreover, although Mad1p and Mad2p perform essential mitotic functions during every division cycle in mammalian cells, they are required in budding yeast only when mitosis goes awry [5].
• Furthermore, localization and hyperphosphorylation of BubR1 at kinetochores are dependent on Bub1 and Mad1, but not Mad2 [6].

Biological context of MAD1

• We have cloned the MAD1 gene and show that when it is disrupted yeast cells have the same phenotype as the previously isolated mad1 mutants: they fail to delay the metaphase to anaphase transition in response to microtubule depolymerization [7].
• Deletion of MAD1 or MAD2 did not affect steady-state nucleocytoplasmic distribution of a classical nuclear localization signal-containing reporter, a nuclear export signal-containing reporter, or Ran localization [8].
• Mad1p becomes hyperphosphorylated when wild-type cells are arrested in mitosis by benomyl treatment, or by placing a cold sensitive tubulin mutant at the restrictive temperature [7].
• We discuss the possible functions of Mad1p at this cell cycle checkpoint [7].
• We conclude that Mad1 and Mad2 are required to detect bipolar orientation and/or tension at kinetochores, whereas Mad3 is not [9].

Anatomical context of MAD1

• In yeast and mammalian cells, the spindle assembly checkpoint proteins Mad1p and Mad2p localize to the nuclear pore complex (NPC) during interphase [8].

Associations of MAD1 with chemical compounds

• We showed using photobleaching analysis that in nocodazole-arrested cells Mad1p rapidly cycles between the Mlp proteins and kinetochores [10].

Physical interactions of MAD1

• On the basis of these results and genetic analysis of double mutants, we propose a model in which Mad1p bound to a Nup53p-containing complex sequesters Mad2p at the NPC until its release by activation of the spindle checkpoint [11].
• Mouse homologs of SIN3 have been identified through screens for proteins interacting with the mammalian Mad1 protein, a transcriptional repressor [12].

Enzymatic interactions of MAD1

• In addition, Mad2p binds to all of the different phosphorylated isoforms of Mad1p that can be resolved on SDS-PAGE [13].

Regulatory relationships of MAD1

• Here, we show that budding yeast Mad1p has a regulated association with Bub1p and Bub3p during a normal cell cycle and that this complex is found at significantly higher levels once the spindle checkpoint is activated [14].

Other interactions of MAD1

• In budding yeast, the Mad1, 2, 3, and Bub1, 2, 3 proteins mediate this arrest [15].
• Checkpoint arrest in the absence of bipolar orientation and tension (induced by replication block in a cdc6 mutant) was lacking in cells without MAD1 or MAD2 [9].
• In budding yeast, Mad1, Mad2, and Mad3 proteins are equally required for arrest in the presence of damage induced by antimicrotubule drugs or catastrophic loss of spindle structure [9].
• Unlike cells delayed in mitosis by spindle damage or MPS1 kinase overexpression, hyperphosphorylated forms of the Mad1p checkpoint protein did not accumulate [16].
• Mutation of this motif abolishes checkpoint function, indicating that formation of the Mad1p-Bub1p-Bub3p complex is a crucial step in the spindle checkpoint mechanism [14].

Analytical, diagnostic and therapeutic context of MAD1

• Anti-Mad1p antibodies give a novel punctate nuclear staining pattern and cell fractionation reveals that the bulk of Mad1p is soluble [7].
• Gel filtration and co-immunoprecipitation analyses reveal that Mad2p tightly associates with another spindle checkpoint component, Mad1p [13].
• Although Mad1 (a basic helix-loop-helix leucine zipper [bHLH-Zip) protein) forms a heterodimer with the Max bHLH-Zip protein, LexA-Mad1 and VP16-Max do not activate transcription of a reporter gene in a two-hybrid assay [12].

References