Trypanosoma cruzi: Suppression of tuzin gene expression by its 5 '-UTR andspliced leader addition site

The genome of the protozoan parasite Trypanosoma cruzi contains a tandemly repeated array of two alternating genes, one encoding amastin and the other encoding tuzin. Amastin is an abundant amastigote surface protein, whereas tuzin is thought to be a rare protein whose location and function are unkn own. The 137-nucleotide 5' untranslated region (5'-UTR) of the tuzin mRNA h as a 22-codon open translation reading frame containing 3 methionine codons followed by a stop codon that overlaps the methionine start codon of the t uzin coding region. A fragment containing the tuzin 5'-UTR and upstream int ergenic region was placed in front of a luciferase reporter gene in a plasm id for transient transfection assays of luciferase activity. By mutating th e three upstream ATGs in the tuzin 5'-UTR and replacing the tuzin spliced l eader (SL) acceptor site with that of the amastin gene, we found that the 2 2-codon reading frame and the tuzin SL acceptor site combine to substantial ly reduce expression of the luciferase gene. These results indicate that ex pression of the multicopy tuzin gene is posttranscriptionally suppressed by both inefficient RNA processing and poor translation initiation, resulting in a low level of tuzin. (C) 1999 Academic Press.