For the grey-scale scheme of sequence identities, TcAAAP amino acid sequences were aligned using the clustalw method and this information was the input for a short routine programmed in perl. Amino acids letters were replaced by grey-scale coloured

lines, where dark tones indicate a low-identity position. To identify gene candidates coding for arginine Roscovitine permeases belonging to the TcAAAP family, 11 of about 34 genes, according to the Tritryps genome project (Berriman et al., 2005), were tested using a yeast model. All available TcAAAP sequences were first analysed, and haplotypes, incomplete sequences and pseudogenes discarded. Using a phenogram constructed from a global sequence alignment and the clustalw algorithm, about one representative member was selected from each cluster of the tree. This ‘rational’ approach was applied to reduce the number of genes analysed. After selection in SC medium, the transformants were AUY-922 functionally

tested for their ability to grow in a medium containing canavanine, an arginine-toxic analogue. Canavanine resistance in yeasts results from a deletion in the gene coding for a specific arginine permease (Can1p) (Grenson et al., 1966). As Fig. 1a shows, adding canavanine in the selection medium, one clear candidate gene (named TcAAAP411) restored the canavanine toxicity in all complementation assays performed. However, a second candidate TcAAAP545 presented slight growth differences with control,

and was also included for further characterization. Canavanine sensitization in yeast could result from various aspects of arginine metabolism other than transport systems. To determine whether TcAAAP411 and TcAAAP545 are actually arginine permeases, the accumulation of radiolabelled l-arginine was analysed. Selected transformant yeasts (TcAAAP545 and TcAAP411) were compared with those transformed with an empty plasmid (pDR196) or with a permease gene in which the resistance was not reversed (TcAAAP069). The initial rate of arginine transport in pDR196, TcAAAP069 and TcAAAP545 showed similar values (1.50, 1.16 and 1.43 pmol min−1 per 107 cells, respectively), whereas in TcAAAP411 arginine uptake was more than threefold higher and increased linearly over time (4.60 pmol min−1 per 107 cells; Fig. 1b). The many expression of TcAAAP411 mRNA was also confirmed by reverse transcriptase-PCR. The TcAAAP family includes >30 sequences, with 34 according to the genome data, but the real gene number is difficult to determine as this genome project remains unfinished and a few putative TcAAAP genes have been classified as ‘unknowns’, pseudogenes or haplotypes variants. In addition, the first bioinformatic characterization of this family was made before the completion of the T. cruzi genome, using only unassembled single-read sequences (Bouvier et al., 2004). Figure 2a is a sequence identity colour-based scheme constructed using all available TcAAAP genes. As Fig.