A nucleic acid that is a target of retrovirus integration and has a substantially palindromic sequence that includes a motif sequence: 5'-.alpha..sub.1-.alpha..sub.2- . . . -.alpha..sub.n-X-.beta..sub.n- . . . -.beta..sub.2-.beta..sub.1-3', wherein .alpha..sub.1 to .alpha..sub.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, .beta..sub.1 to .beta..sub.n each represent a sequence consisting of 4 to 7 bases substantially complementary, in the opposite direction, to the sequence .alpha..sub.1 to .alpha..sub.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 .alpha..sub.1 to .alpha..sub.n and .beta..sub.1 to .beta..sub.n; and upstream and downstream sequences adjacent to the motif sequence, having a length of 2 bases or more.