Splicing of RNA in Eukaryotes

The splicing reaction is remarkably precise cuts are made at unique positions in transcripts that contain 

Base sequence studies of the regions adjacent to several hundred different introns indicate that common sequences can be found at each end of an intron. The sites at which cutting occurs are always 5 to GU and 3 to AG. The rule is that the base sequence of an intron begins with GU and ends with AG. 

Introns are excised one by one, and ligation occurs before the next intron is excised thus, the number of different nuclear RNA molecules present at any instant is huge. Translation does not occur until processing is complete. 

Translated Eukaryotic Genes in Which Introns Have Been Demonstrated 

Diagram of the conalbumin primary transcript and the processed mRNA. The 16 introns, which are excised from the primary transcript, are shown in color. 

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