FIG. 6.

Msp2 expression site variability increases in persistent cattle infection. The variability of each population was calculated over the hypervariable region of the msp2 expression site using the seven independent clones sampled from each of the seven A. marginale populations in Fig. 1, the sequence alignment in Fig. 5, and the following formula: number of different amino acids at a given position/frequency of the most common amino acid at that position. For example, at position 7 in population okcul there is H (histidine) in six clones and Y (tyrosine) in one clone of the msp2 expression site, for a variability of 2/0.857 (=2.3). Values were obtained similarly for all variable positions in the alignment and added, to obtain a total population variability for okcul of 163.8.