TRYPANOSOMA-CRUZI TRANS-SIALIDASE GENE LACKING C-TERMINAL REPEATS AND EXPRESSED IN EPIMASTIGOTE FORMS

Infective trypomastigote forms of Trypanosoma cruzi express an oligomeric trans-sialidase that contains a long stretch of 12-amino-acid repeats at the C terminus, while the insect epimastigote forms have a monomeric trans-sialidase without repeats. Here we show that messenger RNAs encoding trans-sialidases containing the repeats are not present in epimastigotes but are abundant in trypomastigotes. In contrast, mRNA species encoding the conserved N-terminal domain are detected in epimastigotes. A cDNA clone derived from epimastigote mRNA was isolated and characterized. It predicts a repeat-minus amino-acid sequence that has 84% identity to the conserved N-terminal domain of trypomastigote trans-sialidase, and contains some of the necessary amino acids for the catalytic activity, as shown by fusion experiments. Transcripts corresponding to this clone were detected in epimastigotes and in trypomastigotes by reverse-transcriptase and polymerase chain reaction. In addition, the lack of repeats is not due to RNA processing because the corresponding gene without repeats was amplified from the parasite DNA. These results suggest that a distinct set of genes encode the repeat-minus trans-sialidase, and only these trans-sialidase genes are expressed in epimastigote forms.