FIG. 2.
Isolation of pools with mutated PRM. (A) Sequence of the PRM promoter, inverted from the usual order of the λ map. Locations of OR3 and the end of OR2 are shown in bold; the −35 and −10 regions of PRM are underlined; the N′s represent positions that were randomized. Above the sequence is that of a consensus promoter; positions in which PRM differs are underlined. (B) Genetic crosses. λ Δ(PRM) was crossed with a pool of cells containing PRM variants made as previously described (see Materials and Methods and Results). Maps of the OR region in plasmids and phages are to scale. The dashed line between the two parents shows the double crossover yielding the desired recombinant, shown at the bottom. Ns and Bg, NsiI and BglII, respectively. (C) Selection and enrichment for cross progeny forming stable lysogens with a set point near the wild type (see text for details) m.o.i., multiplicity of infection.