cdc13 (SPBC582.03, P10815) review notes

Identity / overview

Cdc13 is the major mitotic B-type cyclin of fission yeast, the regulatory partner of the Cdc2/CDK1 kinase (together = MPF). Cyclin AB subfamily (UniProt). Essential gene; required for the G2/M transition and for mitotic and meiotic nuclear divisions. Targeted for destruction by APC/C at anaphase (classic cyclin behaviour).

Core function evidence

• Cyclin / G2/M control: PMID:2908246 and PMID:2908246
• Forms stable complex with Cdc2 and regulates kinase activity/localization: PMID:2569363 and PMID:2569363
• Cyclin destruction at mitosis: PMID:2534559
• Required to localize Cdc2 to nucleus: PMID:2534559
• CAK Thr167/cyclin association: PMID:1655416

Localization

• Nuclear protein, distinct from chromatin: PMID:2534559
• Nucleus + spindle pole body populations: PMID:1699136
• SPB enrichment in G2, spindle in mitosis; leaves spindle before anaphase: PMID:11683390
• Cytoplasmic pool in interphase, relocalizes to nucleus in mitosis (EM/IF): PMID:8688826
• Hydrophobic patch targets Cdc13 to SPB (centrosome equivalent): PMID:32084401 Wild-type localization: PMID:32084401
• Cut8/proteasome localizes degradation to nucleus/nuclear periphery: PMID:11084332
• Spindle midzone Klp9/Ase1 phospho-regulation by Cdc2: PMID:19686686
• Stationary phase / nucleolar accumulation of CDK: PMID:37128864
• Heat-stress reversible aggregation into nucleolar rings (cell-cycle regulators sequestered): PMID:33176152
• Telomere bouquet/SPB: PMID:29123917

Replication origins / preventing re-replication

PMID:12419251

DNA damage checkpoint / recombinational repair in G2

PMID:12023299

Chromosome bi-orientation

• CPC/Survivin phosphorylation: PMID:20739936
• Merotelic correction via spindle elongation: PMID:22264609

Meiosis (genuine roles, not SPKW over-annotation)

• Required for meiosis I and II nuclear divisions: PMID:25891897 Single complex sufficient: PMID:25891897
• Mes1 blocks Cdc13 degradation to allow MII (negative regulation of meiotic cell cycle progression via Cdc13 stability): PMID:15791259
• Mfr1/APC degrades Cdc13 at end of MII before sporulation: PMID:11493649 mfr1 null retains high Cdc13/Cdc2 activity and delays sporulation: PMID:11493649

Regulation by rum1 (CDK inhibitor)

PMID:9303310

GO annotation assessment summary

• MF core: cyclin-dependent protein serine/threonine kinase regulator activity (GO:0016538) and activator activity (GO:0061575) — ACCEPT as core. Both are well supported.
• BP core: regulation/positive regulation of G2/M transition (GO:0010389, GO:0010971) — ACCEPT/core; meiotic nuclear division (GO:0140013) and negative regulation of meiotic cell cycle (GO:0051447, via Mes1-stabilized pool) — genuine, KEEP (non-core or accept).
• CC: nucleus (core), SPB / mitotic spindle pole body, mitotic spindle, spindle midzone — well supported. Chromatin/telomeric repeat (replication-origin association), nucleolus, nucleolar peripheral inclusion body (stress), nuclear periphery — accept as context.
• "protein binding" (GO:0005515) — uninformative; recommend MODIFY toward cyclin-dependent protein kinase regulator activity where the partner is Cdc2/rum1/Mes1, or KEEP_AS_NON_CORE. Per curation guidelines avoid bare protein binding.
• IBA "traversing start control point" (GO:0007089) and "G1/S transition" — Cdc13 is the mitotic cyclin; primary role is G2/M not Start. The fusion/HPM work shows Cdc13 CAN drive S-phase when it is the only cyclin, but in WT cells G1/S is executed by cig1/cig2/puc1. Treat Start/G1S IBA as non-core / over-annotation for the endogenous mitotic role.

Verbatim quote check (against cached publications, 2026-06)

• 2569363: "The products of the cdc13+ and cdc2+ genes form a stable complex that displays protein kinase activity in vitro." and "these observations suggest that the cdc13+-encoded cyclin acts to regulate both the catalytic properties and the localization of the protein kinase of which it is a subunit." (note: actual text begins "These observations suggest that...")
• 12419251 verbatim: "We show that in fission yeast the mitotic B type cyclin Cdc13/Cdc2 kinase associates with replication origins in vivo. This association is dependent on the origin recognition complex (ORC)".
• 12023299 verbatim: "the major Schizosaccharomyces pombe CDK, Cdc2-cyclin B, influences recombinational repair of radiation-induced DSBs during the G(2) phase at two distinct stages."
• 11084332 verbatim: "destruction of mitotic cyclin and Cut2 in the nucleus is dramatically delayed, though polyubiquitination of Cdc13 occurs in cut8 mutant."
• 29123917 verbatim: "delayed accumulation of CDK1Cdc13 at the SPB" (Cdc13 is superscript in source).
• 8688826 verbatim: "evidencing cytoplasmic localization of p56cdc13, in addition to the nuclear localization previously observed".
• 37128864 verbatim: "Cdc2 accumulates in the nucleolus."
• 33176152 verbatim: "NuRs sequester essential factors required for nuclear mRNA metabolism and nuclear pore complex function, as well as cell-cycle regulators."
• 9472012: rum1/SIC1 are "specific inhibitors of p34(cdc2/CDC28) kinase complexes with B-type cyclins" — binding to the Cdc13-Cdc2 complex; uninformative GO:0005515 IPI, MODIFY toward kinase regulator activity context / KEEP_AS_NON_CORE.
• 26131711: protein binding IPI with Cut1(?) PomBase:SPBC11B10.09 = cdc2; describes two Cdc2 pools in DDR. Uninformative bare protein binding.