The Nuclear PolyA-Binding Protein Nab2p Is Essential for mRNA Production

• Rapid nuclear depletion of polyA-binding protein Nab2p elicits global mRNA decline
• Cells compensate and restore mRNA levels after long-term Nab2p depletion
• mRNA loss is post-transcriptional and depends on polyadenylation
• mRNA decay upon Nab2p depletion is facilitated by the nuclear RNA exosome

SummaryPolyadenylation of mRNA is a key step in eukaryotic gene expression. However, despite the major impact of poly(A) tails on mRNA metabolism, the precise roles of poly(A)-binding proteins (PABPs) in nuclear mRNA biogenesis remain elusive. Here, we demonstrate that rapid nuclear depletion of the S. cerevisiae PABP Nab2p leads to a global loss of cellular mRNA, but not of RNA lacking poly(A) tails. Disappearance of mRNA is a nuclear event, but not due to decreased transcription. Instead, the absence of Nab2p results in robust nuclear mRNA decay by the ribonucleolytic RNA exosome in a polyadenylation-dependent process. We conclude that Nab2p is required to protect early mRNA and therefore constitutes a crucial nuclear mRNA biogenesis factor.

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