Estructura secundaria y mapa de variabilidad de la subunidad pequeña del ARNr de Entamoebaposibles implicaciones para la taxonomía del género

Résumé

The molecular taxonomy of the genus Entamoeba based on sequence comparisons of the small subunit rRNA (16S-rRNA) is confused as there are different criteria regarding the number and importance of the sequence differences for species or subspecies identification. In the present work we analyze the importance of the sequence differences and we identify the regions that could be potentially useful for taxonomic studies. We propose a secondary structure model of the Entamoeba 16S-rRNA obtained by homology modeling after analysis of 25 complete sequences belonging to 19 species. From this model we have determined the variability map of this gene this allowing the identification of the helices accumulating most of the substitutions. These helices are located far from the mRNA and tRNA interaction sites in the tertiary structure. The sequence-structure analyses of the variable helices have shown the existence of numerous compensatory base changes (CBCs) between the different species. The accessory helix 45/e1 seems to be a good candidate for taxonomic studies. The relations between the Entamoeba species obtained after CBC comparisons between the analyzed sequences are basically the same that those published in phylogenetic studies where several evolution models have been used