A SHORT INTERSPERSED REPETITIVE ELEMENT PROVIDES A NEW 3' ACCEPTOR SITE FOR TRANSSPLICING IN CERTAIN RIBOSOMAL P2-BETA PROTEIN GENES OF TRYPANOSOMA-CRUZI

Four Trypanosoma cruzi genomic DNA fragments carrying different TcP2 b eta genes have been isolated and sequenced. Three of them had a single TcP2 beta gene, while the 3.8-kb-long DNA segment encoding the TcP2 b eta-H1.8 locus showed two TcP2 beta genes arranged in tandem. These ge nes were physically connected by a 428-bp-long DNA sequence that was a lso located immediately 5' to the first gene and immediately 3' to the second. Comparison of the 4 TcP2 beta gene loci, suggested that the i nsertion of this repeated element originated the duplication of its ta rget sequence, a poly(dT) stretch. Approximately 1200 copies of this s hort sequence, named short interspersed repetitive element (SIRE), wer e found scattered in the genome. Analysis of the 5' non-coding regions of different TcP2 beta mRNAs, and RNA-PCR experiments suggested that the insertion of a SIRE upstream of a TcP2 beta-H1.8 gene introduced a new 3' spliced leader (SL) acceptor site in the TcP2 beta-H1.8 pre-mR NAs, encoded within the SIRE. Consequently, in the mature H1.8 mRNA th e SL sequence is followed by 38 bases directly transcribed from the SI RE. Structural and functional features of this repeated element reveal similarity to the short interspersed repetitive DNA sequences detecte d in the genomes of several microorganisms.