Phasmid Vectors - These vectors are shortened linear A. genomes containing DNA replication and lytic functions plus the cohesive ends of the phage; their middle nonessential segment is replaced by a linearized plasmid with intact replication module. In practice, a plasmid vector contains several tandem copies of the plasmid to make it longer than 38 kb, the minimum size needed for packaging in A. particles.

During construction of the recombinant DNA, one or more copies of the plasmid are deleted from and the DNA insert is integrated into the vector, but generally one copy of the plasmid is retained in the recombinant DNA. Phasmids, both recombinant and unaltered, are packaged in A. particles in vitro and used for infection of appropriate E. coli cells.