UASp regulatory sequences drive expression of step in which the CC domain has been replaced with sequence encoding the 'APH' CC domain (MKQLEKELKQLEKELQAIEKQLAQLQWKAQARKKKLAQLKKKLQA) with a 3' proline as a linker. APH is a synthetic sequence optimized for CC homodimerization in vitro; it homodimerizes in an antiparallel orientation. The coding sequence is tagged at the N-terminal end with EGFP.