ENTAMOEBA-HISTOLYTICA - GENE LINKAGE GROUPS AND RELEVANT FEATURES OF ITS KARYOTYPE

We identified some gene linkage groups in Entamoeba histolytica using a 4-M urea improved transversal alternating field electrophoresis (TAF E) method. Complex rosette-structured DNA molecules were found trapped along the gel lanes, explaining the fuzziness of the patterns. Using several episomal probes, including 16 S, 5.8 S, and 25 S ribosomal (r) Dna genes, an autonomous replication sequence (ARS), and EhVR1, we id entified a complete ribosomal episome linkage group (CELG) at the 1.2- Mb position. Three other incomplete groups were found: IELG-1, formed by EhVR1,16 S, 5.8 S, and 25 S genes; IELG-2 formed by EhVR1, 16 S and 25 S; and IELG-3 formed only by 5.8 S. Ehadh3, Ehpfo, and Ehredox gen es migrated at the 1.8-Mb position, forming the non-ribosomal linkage group, NRLG-1.8, while the Ehenl-1 gene migrated at 1.6 Mb forming the NRLG-1.6 group. Ehhk was located at 1.2, 0.8, and 0.17 Mb in three di fferent groups: NRLG-1.2, IELG-3-0.8, and NRLG-0.17. Putative lineal c hromosomes were also identified using an heterologous telomeric probe. By in situ hybridization experiments, the rDNA and Ehhk genes were lo cated in both nucleus and cytoplasm, while the Ehpfo and Ehredox genes were found mainly in the nucleus. We propose a model hypothezising th at the 16 S and 25 S genes are in a linear molecule, duplicated in two inverted repeats, which may be looped out of the linear DNA to form a n episome probably lacking or not the 5.8 S sequence, which could be a dded later by recombination.