Those modifications made to pre-mRNA molecules before they leave the nucleus; also called nuclear processing. A gene containing three exons (E1, E2, and E3) and two introns (I1 and I2) is diagrammed. RNA polymerase II transcribes the 3′-5′ strand of the gene to form a 5′-3′ pre-mRNA molecule. Next, a methylated cap (MC) is added to the 5′ end of the primary transcript; a poly-A tail is added to the 3′ end. Finally, the introns are removed and the exons are spliced together during reactions that occur within a spliceosome, and the mature mRNA leaves the nucleus. See alternative splicing, Cajal body, cis-splicing, dystrophin, exon, hemoglobin genes, heterogeneous nuclear RNA (hnRNA), intron, methylated cap, polyadenylation, RNA editing, RNA splicing, small nuclear RNAs, snurposomes, spliceosome, transcriptosomes.
Subjects: Genetics and Genomics.