POSSIBLE INTEGRATION OF TRYPANOSOMA-CRUZI KDNA MINICIRCLES INTO THE HOST-CELL GENOME BY INFECTION

Infection with Trypanosoma cruzi is known is known to induce the divis ion of peritoneal macrophages in BALB/c mice. We have demonstrated, by cytogenetic analysis, that accessory DNA elements are associated with the metaphase macrophage chromosomes of such infected macrophages. Th e identification of these accessory DNA elements with T. cruzi DNA is strongly supported by the association of H-3-label with some chromatid s in macrophages previously infected with T. cruzi which had been labe lled with H-3-methyl-thymidine. The karyotyping consistently showed pr eferential associations of T. cruzi DNA with chromosomes 3,6 and 11. A conclusive demonstration of the parasite origin of the integrated DNA came from fluorescein in situ hybridization studies using specific pa rasite DNAs as probes. In order to determine to identity of the insert ed DNA and to investigate the nature of the integration mechanism, Sou thern blot analysis were performed on DNA extracted from both uninfect ed and infected (but parasite-free) macrophages. Hybridizations of Bam HI, EcoRI and TaqI digests of DNA from T. cruzi-infected host cells ar e revealed the presence of a 1.7-kb DNA fragment when probed with kDNA . The covalent association of kDNA with that of the host was confirmed by the fact that AluI and Hinf-I digests of DNA from infected host ce lls produced a number of bands, in a size range of 0.8-3.6 kb, which h ybridized with kDNA minicircles. None of these bands was found in DNA purified from cell-free preparations of the parasite and thus it must be concluded that they represent insertion fragments between parasite and host cell DNA. These results strongly suggest that kDNA minicircle s from T. cruzi have been integrated into the genome of the host cell following infection.