Deletion of the 5' end of the long (Tet-L) transcripts which encode proteins contains a CXXC DNA-binding domain in addition to the catalytic domain that is present in all protein isoforms. The deletion removes the sequence encoding the DNA-binding domain. Tet-L transcripts are not produced in the mutant flies, and short (Tet-S) transcripts are present at about 50% of wild-type levels.