Evidence that poly(A) binding protein C1 binds nuclear pre-mRNA poly(A) tails

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Poly(A) binding protein C1 (PABPC1) is known for cytoplasmic roles in mRNA translation and decay.
• The nuclear function of PABPC1 remains largely uncharacterized, despite its shuttling between the nucleus and cytoplasm.

Purpose of the Study:

• To investigate the nuclear function of PABPC1.
• To determine if PABPC1 interacts with nuclear pre-mRNAs and under what conditions.

Main Methods:

• UV cross-linking in intact mammalian cells to identify direct RNA interactions.
• Immunopurification assays to assess PABPC1 association with poly(A) polymerase.
• Analysis of PABPC1 binding to polyadenylated versus non-polyadenylated pre-mRNAs.

Main Results:

• PABPC1 associates with nuclear pre-mRNAs containing poly(A) tails, similar to PABPN1.
• PABPC1 does not bind non-polyadenylated histone mRNA, confirming the requirement for a poly(A) tail.
• In vivo UV cross-linking demonstrates direct binding of PABPC1 to pre-mRNA poly(A) tails.
• PABPC1 co-immunopurifies with poly(A) polymerase, suggesting recruitment during poly(A) tail synthesis.

Conclusions:

• PABPC1 binds to polyadenylated transcripts early in mammalian mRNA biogenesis.
• These findings elucidate the mechanism of PABPC1 recruitment to newly synthesized poly(A) tails.
• The study provides insights into PABPC1's role in pre-mRNA processing, stability, mRNA trafficking, and the pioneer round of translation.