Figure 1. Evolvability of vlsE is tightly correlated with sequence diversity among the unexpressed vls cassettes.

The level of sequence diversity at individual sites among the unexpressed vls cassettes was tightly correlated with the rate of sequence change at the corresponding sites in vlsE during experimental infections (R² = 0.67, F(1,200) = 403.6, p<0.0001) (data from [21]). Thus, increasing diversity among the unexpressed cassettes will result in a corresponding increase in the antigenic evolvability at VlsE. Sequence diversity among the unexpressed cassettes was calculated as the entropy (bits) at each site in the 15 unexpressed cassette sequences; the rate of sequence change in the vlsE variants during experimental infections in mice was calculated as the entropy (bits) at each site of the 113 expressed antigen sequences. The diversity at vlsE in these data, from immunodeficient mice, results primarily from mutational inputs from the vls cassettes.