Term Name:	U12-type catalytic step 1 spliceosome
Synonyms:	AT-AC catalytic step 1 spliceosome, mammalian U12-type spliceosomal complex B*, mammalian U12-type spliceosomal complex B2, minor catalytic step 1 spliceosome, U12-type activated spliceosome, yeast U12-type spliceosomal complex A1
Definition:	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.
Ontology:	GO: Cellular Component [GO:0071017]    QuickGO    AmiGO