The P1 phage has gained research interest because it can be used to transfer DNA from one bacterial cell to another in a process known as transduction.

This method of in vivo genetic engineering was widely used for many years and is still used today, though to a lesser extent.

It is created by cutting an appropriately sized fragment from a concatemeric DNA chain having multiple copies of the genome (see the section below on lysis for how this is made).

Another consequence of the DNA being cut out of a concatemer is that a given linear molecule can start at any location on the circular genome.

Depending on various physiological cues, the phage may immediately proceed to the lytic phase or it may enter a lysogenic state.

[5] The gene that encodes the tail fibers have a set of sequences that can be targeted by a site specific recombinase Cin.

[1][11][12] This results in numerous copies of the genome being present on a single linear DNA molecule called a concatemer.

After infecting a new cell this terminal redundancy is used by the host recombination machinery to cyclize the genome if it lacks two copies of the lox locus.

[1][13] If two lox sites are present (one in each terminally redundant end) the cyclization is carried out by the Cre recombinase.

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.

[1][16][17] In the 1960s, Hideo Ikeda and Jun-ichi Tomizawa showed the phage's 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.