FIG. 3.

Top. Ter action excises a recombinant prophage from a double lysogen (146). The drawing shows a segment of the bacterial chromosome containing two differently marked λ prophages: λ A⁺ R⁻ and λ A⁻ R⁺. The attachment sites are indicated by zigzag lines, and the cos sites are indicated by the circle-arrowhead symbol. Heteroimmune superinfection of this dilysogen excises and packages the recombinant expected from Ter cleavage of the two cos sites (see the text). (Bottom) Packaging of λ docL DNA from a single lysogen (125, 185). Induction of a lysogen carrying a single prophage that is unable to excise from the bacterial chromosome leads to abundant production of a noninfectious particle carrying the left cohesive end and prophage and bacterial DNA located to the right of cos.