Figure 3.

(A Upper) Map of the replication region of bacteriophage λ (also present in λ plasmids) from the p_R promoter to oriλ. The scale is given in base pairs, the p_R promoter is marked by the thick arrow, putative DnaA boxes are represented by vertical rectangles, and sequences recognized by the O replication initiator (O boxes) and the A+T-rich region are also indicated. (A Lower) The fragment of λ DNA present in the lacZ fusions is indicated, and the orientation of the DnaA-box is marked by arrow (this part of the figure is not drawn to scale). (B) Sequences of the wild-type and scrambled DnaA boxes present in appropriate fusions. (C) The activity of β-galactosidase per single copy of the fusion is presented (in a table form) for both fusions in dnaA⁺ and dnaA-null hosts. It seems that p_R is activated only in the wild-type host harboring the “wild-type” fusion (YES in the table) and that the lack of either functional DnaA protein or DnaA-binding site immediately downstream of p_R results in no activation of the promoter (NO in the table), and the obtained values reflect residual p_R activity.