Figure 26-4: The essential elements for P4 replication. Panel A. Functional domains of the P4 a protein. The grey bar represents the a protein; its functional domains are indicated by the solid and dotted lines below. Highlighted in white is a 120 amino acid region exhibiting sequence similarity to primases of IncI and IncP plasmids. The amino acid consensus sequences of conserved motifs are reported on top, and the amino acid changes affecting the different activities are listed over the arrows. Pri, primase motif conserved among several prokaryotic primases; Zn²⁺, metal binding motif found in other prokaryotic primases and DNA-repair proteins; Mg²⁺, potential metal binding site, has similarity with other DNA and RNA polymerases; NBS, type A nucleotide binding site found in other helicases of small DNA and RNA viruses; the Cnr-r site, defined by Cnr resistance mutations, interacts with the Cnr protein. From (109) with permission. Panel B. Replicon oriI and oriII. Plasmids pGM545 and pGM526 carry the essential P4 regions of the two P4 replicons, ligated to the chloramphenicol resistance gene. Replicon oriI: ori1 and crr sites, and cnr and a genes; replicon oriII: ori2 and crr sites, and a gene. The genes are expressed under plac control. From (103) with permission. Panel C [not shown on web-page companion to text]. The minimal ori1 sequence and the two direct repeats of crr are reported. The type I iterons are boxed. The arrows indicate the orientation and the number above the arrow the position of the first base of each iteron, respective to the first iteron from the left. For ori2, the sequence of the minimal 22 bp region is reported. Above the sequence, the five base substitution that inactivate ori2. (for better image quality, click here for tif image, which may be quite large; may also require screen refreshing plus special software to view; or view larger tif in separate window)

Figure 26-1, Figure 26-2, Figure 26-3, Figure 26-4 ( a,  b ), Figure 26-5, Figure 26-6 ( a,  b,  c ), Figure 26-7,

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