The P{3'en1} entry in FlyBase is used to denote the transgenic construct present in an insertion when it is known that the inserted element is a deleted version of P{en1} (generated during transposition/excision), and where it is known that sequences have been deleted from the 5' end of the P{en1} element (this includes cases where a single 3' terminal repeat is all that remains). For details of what portion of the original P{en1} element remains for an individual insertion of P{3'en1}, see the description in the insertion report and/or in any allele reports associated with that insertion.