THE SERUM RESISTANCE-ASSOCIATED (SRA) GENE OF TRYPANOSOMA-BRUCEI-RHODESIENSE ENCODES A VARIANT SURFACE GLYCOPROTEIN-LIKE PROTEIN

In the Trypanosoma brucei species, T. b. rhodesiense and T. b. gambien se represent the human infective host range variants, while T. b. bruc ei is lysed upon exposure to a cytotoxic factor in normal human serum. T. b. rhodesiense can occur in a serum-resistant and a serum-sensitiv e form. The resistance towards normal human serum was shown to be a la bile character and to be determined by the environment in which the pa rasites live. We have clearly demonstrated the presence of RNA transcr ipts unique to the resistant forms of T. b. rhodesiense. These transcr ipts encode a protein with VSG characteristics. The DNA fragment isola ted previously, which hybridises with the resistance-specific mRNA seq uence, appears to be a pseudogene belonging to the same gene family.