Comparative Study of the Ribosomal RNA fromLeishmaniaandTrypanosoma1

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Abstract
The ribosomal RNA from several stocks of the genera Leishmania and Trypanosoma were studied by gel electrophoresis, sedimentation on sucrose density gradients and RNA/DNA hybridization experiments. Three major components were observed after electrophoresis in polyacrylamide gels (PAGE-SDS [sodium dodecyl sulfate]), the relative molecular masses being respectively: X1 = 0.83 megadaltons, X2 = 0.63 megadaltons and X3 = 0.54 megadaltons for Leishmania RNA; and X1 = 0.86 megadaltons, X2 = 0.78 megadaltons, and X3 = 0.58 megadaltons for Trypanosoma RNA. Depending upon the isolation procedure, a 4th component, X0 = 1.2 megadaltons (26S), became evident. The later component was purified from L. brasiliensis (Y) by centrifugation on a linear 15-30% sucrose density gradient. This component, after heat denaturation and PAGE-SDS, gave rise to 2 bands coinciding in molecular mass with those of X2 and X3, indicating that these components are part of the large ribosomal subunit whereas X1 belongs to the small one. The above mentioned differences in mobilities of components X1 and X2 between the two genera were no longer observed after electrophoresis in denaturing agarose-formaldehyde gels, suggesting secondary structural differences among these RNA species. Hybridization experiments with L. brasiliensis (Y) DNA showed that both RNA types compete equally well for the ribosomal sites in this DNA, and that L. brasiliensis (Y) rRNA recognizes the ribosomal sites in DNA of T. cruzi (EP); no gross changes occurred in their nucleotide sequences during evolution.