Abstract: A nucleic acid that is a target of retrovirus integration and has a substantially palindromic sequence that includes a motif sequence: 5?-?1-?2- . . . -?n-X-?n- . . . -?2-?1-3?, wherein ?1 to ?n each represent a sequence consisting of contiguous 4 to 7 bases in 5?-CACAGTG-3? or 5?-CACTGTG-3?, X represents an arbitrary sequence consisting of 0 to 10 bases, ?1 to ?n each represent a sequence consisting of 4 to 7 bases substantially complementary, in the opposite direction, to the sequence ?1 to ?n, respectively, n represents an integer of 1 or more, and an arbitrary sequence consisting of one to a few bases may be present between the adjacent sequences among the sequences ?1 to ?n and ?1 to ?n; and upstream and downstream sequences adjacent to the motif sequence, having a length of 2 bases or more.