has part U2-type spliceosomal complex U2 snRNP U6 snRNP U2-type catalytic step 1 spliceosome cellular_component A spliceosomal complex that is formed by the displacement of the U1 and U4 snRNPs from the precatalytic spliceosome; the U2, U5 and U6 snRNPs remain associated with the mRNA. This complex, sometimes called the activated spliceosome, is the catalytically active form of the spliceosome, and includes many proteins in addition to those found in the U2, and U5 and U6 snRNPs. yeast U2-type spliceosomal complex A1 GO:0071006 mah mammalian U2-type spliceosomal complex B2 U2-type activated spliceosome GT-AG catalytic step 1 spliceosome mammalian U2-type spliceosomal complex B* major catalytic step 1 spliceosome 2009-07-30T12:00:35Z catalytic step 1 spliceosome