has part U12-type spliceosomal complex U6atac snRNP U12 snRNP catalytic step 1 spliceosome U12-type catalytic step 1 spliceosome yeast U12-type spliceosomal complex A1 mammalian U12-type spliceosomal complex B* cellular_component mah GO:0071017 AT-AC catalytic step 1 spliceosome mammalian U12-type spliceosomal complex B2 minor catalytic step 1 spliceosome U12-type activated spliceosome 2009-07-30T12:00:35Z A spliceosomal complex that is formed by the displacement of the U11 and U4atac snRNPs from the precatalytic spliceosome; the U12, U5 and U6atac 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 U12, and U5 and U6atac snRNPs.