 P1 can also be used to create the P1-derived artificial chromosome cloning vector which can carry relatively large fragments of DNA.P1 encodes a site-specific recombinase, Cre, that is widely used to carry out cell-specific or time-specific DNA recombination by flanking the target DNA with "loxP" sites (see Cre-Lox recombination).The virion is similar in structure to the T4 phage but simpler.