FIG. 1.

(a) Nucleotide divergence (Pi) of the alignment of 93 wsp sequences. Four peaks are identified, corresponding to the four HVRs. (b) Pattern of distribution of recombination events along the alignment of the 40 wsp nucleotide sequences, as detected by the MAXCHI program. The cumulative number of recombination events per site is given. Notably, all sites encompassing a single HVR experience similar numbers of events, suggesting that single HVRs are generally exchanged as unique tracts. HVR3 and -4 clearly appear to have undergone a proportionally higher number of recombination events than HVR1 and -2.