African trypanosomes express different surface antigens sequentially in their mammalian hosts1. Expression of different variable surface glycoprotein (VSG) antigens is associated with rearrangements of genomic DNA2-5. Several laboratories have reported that expression of some VSG genes is accompanied by the appearance of a duplicated copy of the genes at a new location in the genome3,4. However, in a series of sequentially related Trypanosoma brucei clones from a different stock we were unable to detect duplication of one VSG gene (ILTAT 1.2, B) in expressing clones. Two copies of this gene were found in expressing and non-expressing clones. Apparent insertions and deletions occurred near the 3′ ends of both gene copies, but could not be correlated with expression2,5,6. We report here the observation of both types of rearrangement for different VSG genes in the same series of trypanosome clones. Thus the different types of rearrangement are not a function of different trypanosome stocks, but of different VSG genes within a stock.
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