Gene duplication and transposition linked to antigenic variation in Trypanosoma brucei.

DNA sequence complementary to Trypanosoma brucei mRNAs coding for the synthesis of the variant-specific antigens AnTat 1.1 and AnTat 1.8 have been cloned and characterized. These sequences have been used as probes to analyze the corresponding genes in the nuclear DNA. The two genes seem to be represented in several (three to six) copies, some of which are incomplete. Transcription of one or the other of these two genes is linked to a genetic rearrangement implying duplication and transposition of the "basic" coding sequence. There is probably one additional copy of each gene, and it seems to be complete. The 3' end of each cloned sequence contains, within a 300-base-pair fragment, a genetic element that seems to be repeated and widely distributed in the genome. This repetitive sequence is variant specific. The expression-linked copy of the gene is lost in the culture (procyclic) form of the trypanosome, where the synthesis of variant-specific antigens is shut down. Comparison of two different cloned populations expressing the same serotype (AnTat 1) showed that the recurrence of a given antigenic type may be accompanied by the production of the same additional copy.