AUTONOMOUSLY REPLICATING SINGLE-COPY EPISOMES IN TRYPANOSOMA-BRUCEI SHOW UNUSUAL STABILITY

We have obtained several autonomously replicating plasmids in procycli c Trypanosoma brucei. Two of these have been analyzed in detail. Both exist as monomeric single-copy episomes, which nevertheless demonstrat e significant stability. These episomes transform procyclics at freque ncies that are at least 60-fold higher than those achieved earlier wit h non-replicating molecules. A modified version of one of these episom es is able to replicate autonomously in bloodstream form T. brucei but it is unstable in this developmental stage of the organism. These epi somes will prove useful as shuttle vectors, in functional complementat ion studies, in the construction of promoter-traps for the isolation o f transcriptional promoters in T.brucei, and importantly, as models fo r the analysis of DNA replication in this ancient eukaryotic lineage.