Nucleolin‐enhanced deadenylation and bulk translation (566.1)

Rate of translation is one of the critical factors, determining protein abundance in a cell. After a pioneer round of translation in which 80S ribosome scans the linear mRNA, a cap‐dependent mRNP closed‐loop is formed for bulk translation. Nucleolin interacts with the PABPC and works together for deadenylation and mRNP closed‐loop formation. Nucleolin interacts to the Pan2/Pan3 and CCR4‐NOT deadenylation complex, indicating nucleolin’s involvement in the mRNA deadenylation. Nucleolin also interacts with the eIF4F translation initiation complex, suggesting another role of nucleolin in translation initiation. We found that an increased level of deadenylated mRNAs is associated with heavy polyribosomes in nucleolin overexpressed cell lines. Together these results indicate that nucleolin‐mediated deadenylation is not followed by mRNA decay, but can lead to the bulk translation by forming poly(A) n ‐less mRNP closed‐loop. We propose that a non‐canonical mRNP closed‐loop lacking poly(A) n tail can be formed by nucleolin for bulk translation. In this model, nucleolin enhances deadenylation of the mRNA and induces the formation of poly(A) n ‐less mRNP closed‐loop by binding dsRNA formed between the mRNA 5’‐ and 3’‐UTR complementary sequences. Nucleolin is proposed as a mediator for the transition from the canonical to non‐canonical poly(A) n ‐less mRNP closed‐loop to enhance the bulk translation.