What happens to eukaryotic mRNA without a poly-A tail?

The presence of a poly-A tail at the 3' end of eukaryotic mRNA plays a critical role in its stability and translation. Without this poly-A tail, mRNA becomes susceptible to rapid degradation. The poly-A tail protects the mRNA from enzymatic degradation in the cytoplasm, allowing it to be translated effectively before it is broken down. Without this protective element, the mRNA molecules are quickly acted upon by exonucleases, leading to their degradation.

The poly-A tail also assists in the export of mRNA from the nucleus and enhances translation efficiency by promoting interactions with the translation machinery. Therefore, the lack of a poly-A tail means that the mRNA is not only unstable but also less likely to be translated efficiently. Thus, the option indicating that mRNA without a poly-A tail undergoes rapid degradation accurately reflects the critical function of the poly-A tail in post-transcriptional regulation of gene expression.