The majority of spliceosomes most eukaryotes have includes the U-2 dependent major spliceosome and the less common U12-dependent minor spliceosome. The U2-dependent spliceosome is responsible for removing U2-type introns, which are the most prevalent type. This spliceosome is responsible for the removal of introns during pre-mRNA processing, which is crucial for generating mature mRNA molecules before translation. In contrast, the U12-dependent spliceosome (present in only a subset of eukaryotes) involves the less common U12-type introns. The minor spliceosome performs a similar function to the major spliceosome but targets a distinct subset of introns with different splice site sequences.
Essentially, the U2-dependent spliceosome handles the majority of introns, while the U12-dependent spliceosome deals with a minority of specialized introns. The primary components of the major spliceosome include the five snRNPs, which are composed of snRNAs and numerous associated proteins. The minor spliceosome comprises distinct snRNPs in addition to U12 including U22, U6atac, U4atac which perform functions similar to those in the major-spliceosomal snRNPs. Additionally, both spliceosomes share the U5 snRNP.