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 n ear one telomere of chromosome 35, which are frequently amplified in Leishm ania 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-ex pression, because of their transcription by the RNA polymerase I-mediated r RNA 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 re placement of the three ORFG genes in L. donovani LSB-51.1, ORFG null mutant s were obtained. These mutant cell lines show a direct relationship between ORFG mRNA, protein expression levels and active transport of biopterin int o the cells. Transformation of the null mutant with a plasmid containing OR FG restores biopterin transport activity. In addition, the null mutants are unable to grow in the absence of supplemental biopterin. Thus, ORFG encode s a biopterin transporter and has been renamed BT1. (C) 1999 Elsevier Scien ce B.V. All rights reserved.