P1 was discovered in 1951 by Giuseppe Bertani in Salvador Lurias laboratory, but the phage was little studied until Ed Lennox, also in Lurias group, showed in 1954–5 that it could transduce genetic material between host bacteria. This discovery led to the phage being used for genetic exchange and genome mapping in E. coli, and stimulated its further study as a model organism. In the 1960s, Hideo Ikeda and Jun-ichi Tomizawa showed the phages DNA genome to be linear and double-stranded, with redundancy at the ends. In the 1970s, Nat Sternberg characterised the Cre–lox' site-specific recombination system, which allows the linear genome to circularise to form a plasmid after infection. During the 1980s, Sternberg developed P1 as a vector for cloning large pieces of eukaryotic DNA. A P1 gene map based on a partial DNA sequence was published in 1993 by Michael Yarmolinsky and Małgorzata Łobocka, and the genome was completely sequenced by Łobocka and colleagues in 2004.