3.19—Post-transcriptional changes to mRNA

Eukaryotic pre-mRNA contains coding exons and non-coding introns. Post-transcriptional splicing removes introns and joins exons before the mature mRNA leaves the nucleus.

If the exons are joined in different combinations, alternative splicing produces different mature mRNAs from one gene. Translation of those mRNAs can therefore produce different polypeptides.

The same antibody gene can be spliced to include or omit an exon encoding a membrane-binding region. The resulting protein is either cell-bound or secreted, even though the original gene is the same.

Alternative splicing changes the RNA message after transcription; it does not alter the DNA base sequence. Do not confuse intron removal with DNA replication or mutation.