Posttranscriptional RNA processing refers to a complex set of molecular events that occur after the synthesis of RNA molecules from DNA templates during transcription. It encompasses a series of modifications and processing steps that are necessary for the maturation, functionality, and stability of RNA molecules before they can perform their designated role in the cell.
During posttranscriptional RNA processing, the initial transcript, called precursor RNA or pre-mRNA, undergoes several modifications to generate a mature RNA molecule ready for translation. These modifications include 5' capping, 3' polyadenylation, and RNA splicing.
The process begins with the addition of a modified nucleotide cap at the 5' end of the pre-mRNA molecule, which protects the RNA from degradation and aids in translation initiation. Simultaneously, the pre-mRNA molecule undergoes 3' polyadenylation, where a long chain of adenine nucleotides is added at its 3' end. This poly(A) tail plays a crucial role in regulating mRNA stability and nuclear export.
Furthermore, posttranscriptional RNA processing involves the removal of non-coding regions called introns through a process known as RNA splicing. Introns are excised from the pre-mRNA molecule, leaving only the coding regions called exons, which are then ligated together. This step ensures that the correct sequence of coding regions is maintained before the mature mRNA molecule exits the nucleus.
In addition to these modifications, posttranscriptional RNA processing also includes other processes such as RNA editing, alternative splicing, and RNA localization, which further contribute to the complexity and diversity of RNA molecules in different cell types and conditions.
Overall, posttranscriptional RNA processing plays a vital role in fine-tuning gene expression by regulating RNA stability, transport, and
