The Leishmania donovani LD1 locus gene ORFG encodes a biopterin transporter (BT1).

We have previously described two genes, ORFF and ORFG, from the LD1 locus near one telomere of chromosome 35, which are frequently amplified in Leishmania isolates. In Leishmania donovani LSB-51.1, gene conversion of the rRNA gene locus on chromosome 27 with these two genes resulted in their over-expression, because of their transcription by the RNA polymerase I-mediated rRNA promoter. The predicted ORFG protein has substantial sequence homology to the ESAG10 gene product from the Trypanosoma brucei VSG expression site and both are putative membrane proteins. Using successive rounds of gene replacement of the three ORFG genes in L. donovani LSB-51.1, ORFG null mutants were obtained. These mutant cell lines show a direct relationship between ORFG mRNA, protein expression levels and active transport of biopterin into the cells. Transformation of the null mutant with a plasmid containing ORFG restores biopterin transport activity. In addition, the null mutants are unable to grow in the absence of supplemental biopterin. Thus, ORFG encodes a biopterin transporter and has been renamed BTI.