Molecular biology studies of tubercidin resistance in Trypanosoma cruzi.

Trypanosomatids are incapable of de novo purine synthesis; purines are obtained through the scavenging of exogenous nucleosides. To advance our understanding of purine utilization, we mutagenized a Trypanosoma cruzi stock and selected for resistance to high levels of tubercidin (7-deazaadenosine, TUB), a purine analog. The TUB-resistant stocks were > 100 times more resistant to TUB than was the parental stock. TUB and uridine transport in the TUB-resistant stocks decreased by 50%-90%, whereas thymidine and adenosine transport were unaffected. These data imply that TUB-resistant stocks have defects in the pathways involved in the transport of TUB and uridine but not in the thymidine and adenosine transport pathways. Karyotype analyses using specific probes showed that the deletion of a 950-kb chromosome-size DNA occurred in both of the TUB-resistant stocks. These data suggest that genes involved in nucleoside transport are located in this DNA region. This study will facilitate the identification and characterization of the specific genes involved in nucleoside transport and aid in the elucidation and development of new chemotherapeutics for Chagas' disease.