An Overview of mRNA Processing
After being transcribed from DNA by RNA polymerase II in the nucleus, immature messenger RNAs (mRNAs), known as pre-mRNAs undergo three major processing steps prior to reaching functional maturity1. The mature mRNAs are then transported to the cytoplasm for translation to protein. At each processing step, the mRNA is bound by various RNA-binding proteins and non-coding RNAs, and packaged into large complexes called ribonucleoprotein particles (mRNPs) that assemble during transcription. These complexes control the genesis, function, and eventual degradation of the mRNA2.
The first step of RNA processing, termed capping, occurs as a new pre-mRNA emerges from RNA polymerase II. A guanine nucleotide is added to the 5' end of the pre-mRNA and then methylated. The presence of the cap protects the mRNA from degradation3. During splicing, regions of mRNA sequences not expressed in proteins (introns) are excised and the remaining exons are joined together in a molecular machine termed the spliceosome4. In the final step of RNA processing, called polyadenylation, several adenosine nucleotides are added to the 3' end of the mRNA, which helps to prevent degradation and promotes export from the nucleus to the cytoplasm4.
After processing, export to the cytoplasm occurs through nuclear pore complexes. Although the exact mechanism of export remains unknown, one component of this process involves contact between a Serine/Arginine-rich (SR) export adapter located within the mRNP and a TAP-p15 export receptor that promotes translocation through the nuclear pore complex4, 5. Translation of the mRNA to yield the final protein begins once the 5' cap of the mRNA is recognized by the translation initiation factor eIF4A, among others5.
Detection of human Phospho SMC1 (S957) by WB of293T lysate treated with 100 µM etoposide (+) or mock treated (-). Secondary: HRP-conjugated goat anti-rabbit IgG (A120-101P).
Below is the entire list of targets involved with mRNA Processing: