Figure 3.—

The effects of the cosB^λ mutations on packaging efficiency by λ and 21 helpers. Packaging efficiencies are normalized by setting the cognate packaging efficiencies to 1.0. cosB structures are indicated by rectangles: open rectangles indicate cosB^λ and shaded rectangles represent cosB²¹. Dots and squares indicate two base-pair positions that (1) are conserved in all three R sequences of λ and 21 and (2) differ between λ and 21. Dots represent base pair 56 in R3, base pair 117 in R2, and base pair 158 in R1. Open circles represent the λ-specific TA base pair, and solid dots the 21-specific GC base pair. Note that R2 is oriented opposite to R3 and R1, so the R2 base pair is an AT base pair in λ and a CG in 21. Squares represent base pair 59 in R3, base pair 114 in R2, and base pair 161 in R1. Open squares indicate the λ-specific CG base pair, and solid squares the 21-specific GC base pair. Again, because of the opposite orientation of R2, base pair 114 is GC in λ and CG in 21. The dashed lines indicate the approximate relative yield (5% of wild type) required for plaque formation.