Bipolar orientation of chromosomes in Saccharomyces cerevisiae is monitored by Mad1 and Mad2, but not by Mad3.
The spindle checkpoint governs the timing of anaphase separation of sister chromatids. 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. We find that the MAD genes are not equally required for robust growth in the presence of more subtle kinetochore and microtubule damage. A mad1Delta synthetic lethal screen identified 16 genes whose deletion in cells lacking MAD1 results in death or slow growth. Eleven of these mad1Delta genetic interaction partners encode proteins at the kinetochore-microtubule interface. Analysis of the entire panel revealed similar phenotypes in combination with mad2Delta. In contrast, 13 panel mutants exhibited a less severe phenotype in combination with mad3Delta. 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. Cells without MAD3 were checkpoint-proficient. We conclude that Mad1 and Mad2 are required to detect bipolar orientation and/or tension at kinetochores, whereas Mad3 is not.
Lee
Marina S
MS
McKusick-Nathans Institute of Genetic Medicine, School of Medicine, The Johns Hopkins University, Baltimore, MD 21205, USA.
Spencer
Forrest A
FA
D000970:Antineoplastic Agents / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D015825:Chromosomes, Fungal / Q000378:metabolism*; D005656:Fungal Proteins; D018386:Kinetochores / Q000378:metabolism; D064246:Mad2 Proteins; D008870:Microtubules / Q000378:metabolism; D009154:Mutation; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism; D013172:Spores, Fungal / Q000502:physiology
D000970:Antineoplastic Agents; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; C501382:MAD1 protein, S cerevisiae; C577695:MAD2 protein, S cerevisiae; C406764:MAD3 protein, S cerevisiae; D064246:Mad2 Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D015739:Nocodazole