Aspects of the disclosure relate to a nucleic acid comprising a heterologousnucleic acid insert flanked by interruptedself-complementary sequences, wherein one self-complementary sequence isinterrupted by a cross-arm sequence forming two opposing,lengthwise- symmetric stem-loops, and wherein the other of the self-complementary sequences is interrupted by a truncatedcross-arm sequence. Methods of delivering the nucleic acid to a cell are alsoprovided.