Giardia lamblia trophozoites contain multiple alleles of a variant-specific surface protein gene with 105-base pair tandem repeats

Giardia lamblia trophozoites undergo antigenic variation of a variant-specific surface protein (VSP). All VSPs that have been reported have had high cysteine contents, including numerous copies of a CXXC motif. The first vsp gene described (vspA6; from the cloned line, WBA6), contained 21 copies of a 195 base pair tandem repeat, but other reported VSPs have not contained repeats. In this report, we describe the vsp gene from WBC5, a cloned line derived from WBA6. The vspC5 gene contains short 5' and 3' regions flanking 26 copies of a 105-bp tandem repeat, which comprises 93% of the coding region. In addition to the copy containing 26 repeats, the genome contains other copies of the vspC5 with fewer copies of the repeat. The sequences flanking the repeats are identical, and all copies map to the same location on chromosomal Band 5, suggesting that multiple alleles of the vspC5 gene are present.