Poly(A) tail dynamics: Measuring polyadenylation, deadenylation and poly(A) tail length

A Novel Mechanism for Transcription Termination in the mod(mdg4) Locus of Drosophila melanogaster

This study investigated an alternative mechanism of transcription termination that occurs independently of polyadenylation. We focused on a non-canonical transcription terminator (NTT) identified in the mod(mdg4) gene of Drosophila melanogaster. Using a developed model system, we demonstrated that the minimal functional unit of the NTT consists of 79 nucleotides that form a specific secondary RNA structure. Our results indicate that transcripts generated from the NTT exhibit reduced stability and are hindered in their export to the cytoplasm. An NTT from the distantly related species D. willistoni could function as a transcription terminator in D. melanogaster cells, highlighting the importance of conserved motifs for NTT functionality. At the same time, the NTT did not function in human cells, suggesting that the interaction of the NTT with specific protein factors is required to terminate transcription.

Molecular Insights into mRNA Polyadenylation and Deadenylation

Poly(A) tails are present on almost all eukaryotic mRNAs, and play critical roles in mRNA stability, nuclear export, and translation efficiency. The biosynthesis and shortening of a poly(A) tail are regulated by large multiprotein complexes. However, the molecular mechanisms of these protein machineries still remain unclear. Recent studies regarding the structural and biochemical characteristics of those protein complexes have shed light on the potential mechanisms of polyadenylation and deadenylation. This review summarizes the recent structural studies on pre-mRNA 3′-end processing complexes that initiate the polyadenylation and discusses the similarities and differences between yeast and human machineries. Specifically, we highlight recent biochemical efforts in the reconstitution of the active human canonical pre-mRNA 3′-end processing systems, as well as the roles of RBBP6/Mpe1 in activating the entire machinery. We also describe how poly(A) tails are removed by the PAN2-PAN3 and CCR4-NOT deadenylation complexes and discuss the emerging role of the cytoplasmic poly(A)-binding protein (PABPC) in promoting deadenylation. Together, these recent discoveries show that the dynamic features of these machineries play important roles in regulating polyadenylation and deadenylation.