Posttranscriptional

Posttranscriptional refers to regulatory events that occur after an RNA transcript has been synthesized. It encompasses RNA maturation, modification, transport, stability, localization, and translation, shaping transcripts into functional mRNAs and controlling protein production.

In eukaryotes, core RNA processing includes 5' capping, 3' polyadenylation, and splicing to remove introns. Many transcripts also undergo RNA editing and base modifications, and alternative splicing generates multiple protein isoforms from a single gene. Following processing, RNAs are exported from the nucleus to the cytoplasm.

RNA stability and decay determine transcript abundance. Deadenylation often initiates decay, then decapping and 5' to 3' exonuclease digestion. Pathways such as nonsense-mediated decay monitor premature stop codons, while AU-rich elements and microRNAs, together with RNA-binding proteins, influence decay rates.

Translation control and localization are major posttranscriptional layers. Elements in 5' and 3' untranslated regions regulate initiation and efficiency, and mRNAs may be trafficked to specific cellular compartments where translation occurs or is repressed.

Noncoding RNAs and RNA editing contribute further regulation. Adenosine-to-inosine editing by ADAR enzymes can alter codons or RNA structure, and iron regulatory proteins adjust the translation and stability of ferritin and transferrin receptor mRNAs in response to iron.

Posttranscriptional regulation complements transcriptional control, enabling rapid and context-specific adjustments in gene expression. Disruptions of splicing, mRNA decay, or translation are linked to developmental defects and diseases such as cancer and genetic disorders.