A DIFFERENTIALLY EXPRESSED GENE FAMILY ENCODING AMASTIN A SURFACE PROTEIN OF TRYPANOSOMA-CRUZI AMASTIGOTES

A new family of closely related glycoproteins, collectively called ama stins, has been found on the surface of the amastigote form of Trypano soma cruzi. The gene family encoding these amastigote-specific protein s was identified by differentially screening an amastigote cDNA librar y with reverse transcribed poly(A)(+) RNA from amastigote and epimasti gote stages of the parasite. Amastins are encoded by eight or more tan dem genes, at least five of which are distinguished by nucleotide poin t changes. The 1.4-kilobase amastin mRNAs are 50 times more abundant i n amastigotes than in epimastigotes or trypomastigotes. The amastin ge nes are transcribed to an equal extent in both amastigotes and epimast igotes, indicating that the stage-specific amastin mRNA levels are det ermined by a post-transcriptional mechanism. Sequence determination of full-length cDNAs reveals an open reading frame encoding 174 amino ac ids and a 700-base pair 3'-untranslated region. Nascent amastins conta in four distinct hydrophobic regions of 20-30 amino acids each, 2 at i nternal locations and 1 each at the N and C termini.