puc1 (SPBC19F5.01c, UniProt P25009) — curation notes

Identity

Sources available

Biology (synthesis)

  1. Discovery. puc1+ was cloned by complementation of S. cerevisiae cln1 cln2 cln3 (WHI1/DAF1)
    deficiency PMID:1828291; in S. pombe its overexpression gave a
    cyclin-like role distinct from the mitotic B-type cyclin PMID:1828291.
  2. 1994 characterisation. Forsburg & Nurse could not detect a mitotic G1/S function of puc1
    on its own, but found that it acts at the cycling/non-cycling transition: expression rises
    in nitrogen starvation, puc1 affects the timing of sexual development, and overexpression
    blocks sexual development and rescues pat1ts lethal meiosis [PMID:8006074 "We fail to
    identify any function of this cyclin at the mitotic G1/S transition in S. pombe, but
    demonstrate that it does function in exit from the mitotic cycle"; "Overexpression of the
    puc1 protein blocks sexual development, and rescues pat1ts cells, which would otherwise
    undergo a lethal meiosis"].
  3. Redundant G1/S role (Martin-Castellanos et al. 2000, via deep research). puc1 deletion is
    silent alone but in cig1 cig2 background lengthens G1 and raises the size at S-phase entry;
    the triple mutant is ~15% larger; rum1 deletion abolishes the excess G1. Puc1-Cdc2
    immunocomplexes phosphorylate Rum1 T58/T62 and are resistant to Rum1 inhibition, whereas
    Cdc13-Cdc2 and Cig2-Cdc2 are inhibited [file:SCHPO/puc1/puc1-deep-research-falcon.md "Puc1
    and Cdc2 immunocomplexes phosphorylated Rum1 in vitro at Thr58 and Thr62"; "At 10 nM Rum1,
    Cdc2–Cdc13 activity was inhibited and Cdc2–Cig2 activity was almost completely inhibited,
    whereas Puc1-associated activity was not significantly inhibited"]. Puc1 does not drive S
    phase in the absence of cig1, cig2 and cdc13 PMID:8631306.
    This is the Cln3-like "gate-opening" role: relief of Rum1 inhibition so that the B-type
    cyclin-Cdc2 complexes can fire.
  4. Start machinery. Puc1 associates in vivo with the Ran1/Pat1 kinase and the MBF subunit
    Cdc10; Ran1 controls the Puc1-Cdc10 association PMID:9201720. This ties the G1 cyclin to
    both the MBF transcription complex and the meiosis-repressing Pat1 kinase.
  5. Sexual differentiation. Zfs1 (CCCH tandem zinc finger RBP) binds puc1+ mRNA and lowers
    Puc1 levels; in zfs1Δ Puc1 is elevated and mating drops five-fold, and puc1Δ (but not cig1Δ
    or cig2Δ to the same extent) restores mating; Puc1 has a dose-dependent inhibitory effect on
    mating and delays G1 arrest on nitrogen removal [PMID:29084823 "This experiment showed that
    Puc1 has a dose-dependent inhibitory effect over sexual differentiation, with increasing
    levels of Puc1 reducing mating efficiency to the levels observed in the zfs1Δ mutant";
    "Neither cig1+ nor cig2+ gene deletion suppressed the mating defect of the zfs1Δ mutant as
    efficiently as puc1+ gene deletion, indicating a specific role of Puc1 cyclin in the
    phenotype of the zfs1Δ mutant"]. The proposed mechanism is Puc1-Cdc2 phosphorylation of
    Rum1 (and possibly extended inhibitory phosphorylation of Ste11) PMID:29084823.
  6. Meiosis. No specific meiotic role; cig1 cig2 puc1 triple mutants mate and sporulate
    PMID:25891897; puc1 expression is nearly undetectable in meiotic prophase PMID:30640914.
  7. Localization. Only high-throughput data: the ORFeome YFP screen (PomBase HDA rows: nucleus
    and cytosol) PMID:16823372. No targeted localization study exists; the deep research explicitly
    flags localization as unresolved.

Curation decisions (rationale summary)

Open items