The minor spliceosome is a
ribonucleoprotein complex that catalyses the removal (
splicing) of an atypical class of spliceosomal
introns (U12-type) from eukaryotic
messenger RNAs in plant, insects, vertebrates and some fungi (
Rhizopus oryzae). This process is called noncanonical splicing, as opposed to U2-dependent canonical splicing. U12-type introns represent less than 1% of all introns in human cells. However they are found in genes performing essential cellular functions.