Article

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

Department of Biochemistry and Biophysics , University of Rochester, Rochester, New York, United States
Molecular and Cellular Biology (Impact Factor: 4.78). 05/2006; 26(8):3085-97. DOI: 10.1128/MCB.26.8.3085-3097.2006
Source: PubMed

ABSTRACT

In mammalian cells, poly(A) binding protein C1 (PABP C1) has well-known roles in mRNA translation and decay in the cytoplasm.
However, PABPC1 also shuttles in and out of the nucleus, and its nuclear function is unknown. Here, we show that PABPC1, like
the major nuclear poly(A) binding protein PABPN1, associates with nuclear pre-mRNAs that are polyadenylated and intron containing.
PABPC1 does not bind nonpolyadenylated histone mRNA, indicating that the interaction of PABPC1 with pre-mRNA requires a poly(A)
tail. Consistent with this conclusion, UV cross-linking results obtained using intact cells reveal that PABPC1 binds directly
to pre-mRNA poly(A) tails in vivo. We also show that PABPC1 immunopurifies with poly(A) polymerase, suggesting that PABPC1
is acquired by polyadenylated transcripts during poly(A) tail synthesis. Our findings demonstrate that PABPC1 associates with
polyadenylated transcripts earlier in mammalian mRNA biogenesis than previously thought and offer insights into the mechanism
by which PABPC1 is recruited to newly synthesized poly(A). Our results are discussed in the context of pre-mRNA processing
and stability and mRNA trafficking and the pioneer round of translation.

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    • "PAP slowly adds A residues to the new 3′ end until a length sufficient for poly(A)-binding protein nuclear 1 (PABPN1) association is created. PABPN1 association with short poly(A) tails stimulates the rate of polyadenylation by PAP (Kuhn et al., 2009), culminating in a poly(A) tail of roughly 200–250 residues to which both PABPN1 and its largely cytoplasmic counterpart PABPC1 are bound in the nucleus (Hosoda et al., 2006). "
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    • "Although several mitochondrial proteins have been shown previously to bind RNA and poly(A) sequences in mitochondria (43–45), none binds poly(A) tails preferentially. Of the four human PABPC genes, three (PABPC1, PABPC3 and PABPC4) are established polyA-binding proteins (46–48); however, none has a predicted N-terminal MTS based on the annotated first AUG codon, or downstream AUG codon, and only PABPC5 predicts a dATI-dependent mitochondrial isoform. Several lines of evidence provide support for the proposed dATI-mediated mitochondrial isoform of PABPC5. "
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