One form of posttranscriptional modification of most eukaryotic pre-mRNAs is the addition of a poly-A sequence at the 3' end. The absence of a poly-A sequence leads to rapid degradation of the transcript. Poly-A sequences of various lengths are also added to many bacterial RNA transcripts where, instead of promoting stability, they enhance degradation. In both cases, RNA secondary structures, stabilizing proteins, or degrading enzymes interact with poly-A sequences. Considering the activities of RNAs, what might be general functions of 3'-polyadenylation?

Key Concepts

Polyadenylation

Polyadenylation is the process of adding a poly-A tail, a stretch of adenine nucleotides, to the 3' end of an RNA molecule. In eukaryotes, this modification enhances mRNA stability, facilitates nuclear export, and aids in translation initiation. Conversely, in bacteria, poly-A tails can signal for RNA degradation, illustrating the diverse roles of this modification across different organisms.

RNA Stability and Degradation

RNA stability refers to the lifespan of an RNA molecule within a cell, which is influenced by various factors, including modifications like polyadenylation. In eukaryotes, a poly-A tail protects mRNA from degradation by exonucleases, while in bacteria, the presence of poly-A can mark RNA for degradation. Understanding these dynamics is crucial for grasping how gene expression is regulated post-transcriptionally.

RNA Secondary Structures

RNA secondary structures are formed by intramolecular base pairing, leading to various shapes that can influence RNA function. These structures can affect the stability of RNA molecules and their interactions with proteins and enzymes. In the context of polyadenylation, secondary structures can either stabilize the RNA or expose it to degradation pathways, highlighting their role in posttranscriptional regulation.