Pre-mRNA processing takes place in the nucleus. Introns are excised from the pre-mRNA transcript and the exons are ligated (spliced) to generate the mature mRNA. (left - click to enlarge image)
RNA processing events include capping of the 5’ end on the precursor mRNA, pre-mRNA splicing to remove intronic sequences, and polyadenylation of the 3’ end of the pre-mRNA.
Capping of the 5’ end of the nascent pre-mRNA is performed soon after initiation of transcription. Cleavage, pre-mRNA splicing, and polyadenylation usually follow termination of transcription of short primary transcripts with few introns. However, introns often are spliced out of the nascent RNA before transcription of the gene is complete for large genes with multiple introns.  diagram - pre-mRNA processing Џ animation of RNA splicing : animation - mRNA processing : genetics animations  diagram - spliceosome assembly :
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