Caracterizacion molecular de un retrotransposon sin-LTR. Organizacion genomica y modelo de integracion

LlTc is a non-LTR retrotransposon, dispersed throughout the genome of Trypanosoma cruzi, actively transcribed into poly (A)+ RNA. This element has at its 3' end a fragment of a highly repetitive sequence E12 and at its 5'end a ribosomal mobile element-like sequence. A genomic region of T. cruzi CL strain containing 3 copies of LlTc, tandemly organized, has been characterized. Upstream of the genomic region containing the three copies we found repeated sequences as E13 and DGF-I. A genomic region with the same organization and sequences, but lacking LlTc, was found in the Maracay strain. The deduced aminoacid sequence of ORF1 of L1Tc exhibits a significant homology with sequences of the AP endonuclease protein family. The analysis of the activity of the 40Kd recombinant protein, named NL1TC, obtained from the expression of the L1Tc ORF1 in a E. coli in vitro expression system, revealed that the sequence codes for a protein with endonuclease activity. Date are also presented showing that in vivo expression of NL1Tc protein conferred viability by complementation to E. coli exonuclease III deletion mutants (BW286 strain). We propose that NL1Tc generates free 3'OH sites in the chromosomal DNA necessary for LlTc retrotransposition.