Figure 3. Distribution of Chi sites in lambdoid genomes.

Lambdoid genomes (average length of 45 kb) were divided in 5% non-overlapping contiguous intervals (i.e. 2.25 kb). We plotted for each interval the average number of observed Chi motifs per phage. Phages were divided in three classes according to the encoded recombination functions: Rec⁻, Rec⁺Inh⁻ and Rec⁺Inh⁺. Integrases of the Tyrosine recombinase family were detected as in [10]. Each genome was polarized with the integrase on the left end (the few genomes lacking tyrosine recombinase integrases were discarded). A schematic representation of Lambda-like phages is given on top. Label “ori” indicates the median position of the homologs of Lambda gene O, which includes the origin of replication. The label “cos” indicates the median position of the start of the first terminase gene, which is where the cos site is located in Lambda.