λ phage strains

Δrap514 and Δorf432 are deletions of λ base pairs 42,440–43,037 and 40,621–41,073, respectively (Materials and Methods). red3, an unconditional red− allele [108]; gam210, an amber allele suppressible by E. coli SuII+ or SuIII+[109]; imm21cts, phage 21 immunity region substituted into λ with a temperature-sensitive clear-plaque mutation [110]; SR4°, mutation inactivating the λ EcoRI 4 site [111]; χ+D, Chi+ mutation between the λ S and R genes [112]; Sam7, SuIII+-suppressible amber mutation in the essential S gene [113]; XhoI40.4, 18bp insertion containing a XhoI site in the ren gene [11].