has part U2-type spliceosomal complex U1 snRNP U2 snRNP U4/U6 x U5 tri-snRNP complex U2-type precatalytic spliceosome mammalian U2-type spliceosomal complex B mammalian U2-type spliceosomal complex B1 A spliceosomal complex that is formed by the recruitment of the preassembled U4/U6.U5 tri-snRNP to the prespliceosome. Although all 5 snRNPs are present, the precatalytic spliceosome is catalytically inactive. The precatalytic spliceosome includes many proteins in addition to those found in the U1, U2 and U4/U6.U5 snRNPs. yeast U12-type spliceosomal complex A2-1 GT-AG precatalytic spliceosome cellular_component mah GO:0071005 2009-07-30T12:00:35Z major precatalytic spliceosome precatalytic spliceosome