CSTF1

CSTF1 (CstF-50) is a structural subunit of the trimeric cleavage stimulation factor (CstF) complex, where together with the RNA-binding subunit CstF-64/CSTF2 and CstF-77/CSTF3 it is required for recognition of the correct 3'-end processing site and for cleavage/polyadenylation of pre-mRNA (PMID:29673127). Beyond its core role in constitutive 3'-end processing, CSTF1 links RNA 3'-end maturation to the DNA damage response: following UV irradiation, the p53 C-terminus associates with CstF-50 and BARD1, and this p53–BARD1–CstF complex inhibits the 3' cleavage step of polyadenylation in vitro, an inhibition that is lost with a tumor-associated p53 mutation that weakens p53 binding to CstF and BARD1 and is restored by wild-type p53 (PMID:21383700). CSTF1 has also been localized to U2 snRNA gene loci by genomic affinity purification (PMID:35625631).

1. 2011 Medium

   Established that 3'-end processing is coupled to the DNA damage response by showing CstF-50 forms a regulatory complex with p53 and BARD1 that suppresses pre-mRNA cleavage after UV damage.

   Evidence Co-immunoprecipitation from UV-treated cell extracts and in vitro 3' cleavage assay, with a tumor-associated p53 mutant and wild-type rescue

   PMID:21383700

   Open questions at the time

   • The structural basis and direct binding interface between CstF-50 and p53/BARD1 is not resolved
   • Whether this inhibition occurs on endogenous transcripts genome-wide in vivo is not addressed
   • The downstream consequence of cleavage inhibition for DNA repair or cell fate is not established
2. 2018 Medium

   Defined CSTF1/CstF-50 as a non-RNA-binding structural subunit of the trimeric CstF complex required for correct poly(A) site recognition and cleavage, with CstF-64 serving as the RNA-binding subunit.

   Evidence Knockout of the paralog Cstf2t with RNA-seq and A-seq profiling of polyadenylation in male germ cells, establishing complex composition and CSTF1's role by context

   PMID:29673127

   Open questions at the time

   • Direct functional contribution of CSTF1 itself (versus the complex) was inferred by context, not isolated by CSTF1 perturbation
   • Stoichiometry and assembly determinants of the trimer are not addressed here
3. 2022 Low

   Placed CSTF1 at U2 snRNA gene loci, raising the possibility that the polyadenylation machinery participates in snRNA gene transcription/processing.

   Evidence CAPTURE (deadCas9-mediated chromatin affinity purification) of tandem U2 snRNA gene loci followed by mass spectrometry in human cells

   PMID:35625631

   Open questions at the time

   • Single-lab, single pull-down method with no functional consequence linked specifically to CSTF1 at these loci
   • Whether the association is direct or mediated through the CstF complex is unknown

• The molecular mechanism by which CSTF1 specifically contributes to poly(A) site selection within the CstF trimer, and how its DNA-damage-coupled regulation reshapes transcriptome-wide 3'-end processing, remains undefined.
• No structure of the human CstF trimer or of CSTF1 in complex with p53/BARD1 in the corpus
• No CSTF1-specific loss-of-function transcriptome study
• Functional role at snRNA loci uncharacterized