posttranskription

Posttranskription refers to the processes and mechanisms that occur after messenger RNA (mRNA) has been synthesized during transcription in eukaryotic cells. Unlike prokaryotes, where mRNA is typically ready for translation immediately after synthesis, eukaryotic mRNA undergoes several modifications before it can be exported from the nucleus and translated into proteins.

The primary posttranscriptional modifications include the addition of a 5' cap, polyadenylation at the 3' end, and splicing of introns. The 5' cap, a modified guanine nucleotide, protects the mRNA from degradation and aids in its export from the nucleus and binding to ribosomes. Polyadenylation involves the addition of a poly(A) tail, which also stabilizes the mRNA and facilitates its export and translation. Splicing removes non-coding regions called introns and joins coding regions called exons to form a mature mRNA transcript.

Posttranscriptional regulation further controls gene expression by influencing mRNA stability, localization, and translation efficiency. For example, microRNAs (miRNAs) and other small RNAs can bind to mRNA, leading to its degradation or inhibition of translation. Additionally, RNA-binding proteins (RBPs) can modulate mRNA stability, transport, and localization within the cell.

Posttranscriptional processes are critical for ensuring that only properly processed and functional mRNAs are translated into proteins, thereby maintaining cellular homeostasis and responding to environmental or developmental cues. Dysregulation of these processes has been linked to various diseases, including cancer and neurological disorders, highlighting their importance in both normal physiology and pathology.