EXPRESSION AND EVOLUTION OF MEMBERS OF THE TRYPANOSOMA-CRUZI TRYPOMASTIGOTE SURFACE-ANTIGEN MULTIGENE FAMILY

The trypomastigote specific surface antigens of Trypanosoma cruzi are encoded by a supergene family which includes the TSA family. The TSA f amily is characterized by the presence of a 27-bp tandem repeat array in the coding region. Here, we report the characterization and analysi s of the three TSA family members in the Esmeraldo strain of the paras ite. In this strain 2 distinct telomeric members are expressed abundan tly as 3.7-kb mRNAs, while the remaining member is located at an inter nal chromosomal site and is expressed at less than 2% of the level see n for the telomeric members. Based on hybridization to DNA separated b y PFGE, 3 chromosomes of sizes 1.8 Mb, 0.98 Mb, and 0.90 Mb each conta in one of the telomeric members. In addition, the two smaller chromoso mes also contain the single internal member. Since both chromosomes co ntain similar TSA family members, and vary only slightly in size, we s uggest that they are homologues. Comparisons of the nucleotide sequenc es of the different members of the family show that the internal gene differs from the telomeric genes primarily in sequences found 3' of th e repeat array. These comparisons also reveal that the three genes are analogous, supporting the hypothesis that short segments between the family members are exchanged by gene conversion events. We propose tha t similar conversion events between members of different gene families may generate some of the diversity found within the supergene family.