The complete sequence of Plasmodium berghei merozoite surface protein-1 and its inter- and intra-species variability

The complete gene for merozoite surface protein-1 (MSP-1) from Plasmodium berghei has been cloned and sequenced. Comparison of the P. berghei MSP-1 sequence with MSP-1 from other rodent parasites reveals five conserved domains interrupted by four variable blocks. These variable blocks exhibit no sequence homology but do have similar amino acid compositions. Primary proteolytic processing sites are located near the boundaries between the conserved domains and the variable blocks. Sequencing of the variable blocks from several P. berghei isolates shows that the predominant intra-species difference is in the number of tandem repeats. The inter- and intra-species differences suggest that the variable blocks are localized areas with relatively high levels of slipped-strand mispairing, unequal crossing-over, or other intragenic recombination activity. MSP-1 from P. berghei exhibits more repetitiveness than MSP-1 from other species suggesting that P. berghei experiences a higher intrinsic level of events producing variable numbers of tandem repeats or a lower level of events leading to the degeneration of tandem repeats.