For many eukaryotic introns , splicing is done in a series of reactions which are catalyzed by the spliceosome , a complex of small nuclear ribonucleoproteins ( snRNPs ) There are also self-splicing introns . For many eukaryotic introns , splicing is done in a series of reactions which are catalyzed by the spliceosome , a complex of small nuclear ribonucleoproteins ( snRNPs ) , but there are also self-splicing introns .