In molecular biology, a twintron is an intron-within-intron excised by sequential splicing reactions.
[1] They found that splicing of both the internal and external introns occurs via lariat intermediates.
In 1993 a new type of complex twintron composed of four individual group III introns has been characterized.
In 1995 scientists discovered the first non-Euglena twintron in cryptomonad alga Pyrenomonas salina.
[12] Recently, two novel twintrons have been uncovered within the fungal mitochondrial genome, one at position mS917 of the Cryphonectria parasitica mt-rns gene, where a group ID intron encoding a LAGLIDADG ORF invaded another ORF-less group ID intron.