Trypanosoma cruzi ribosomal RNA: internal break in the large-molecular-mass species and number of genes.

The large-molecular-mass ribosomal ribonucleic acid from Trypanosoma cruzi probably contains an internal break. The molecule can be obtained in its intact form or in its two fragments depending on the denaturing agents used for its purification and/or display. This break appears to be an in vivo late processing step rather than a random nucleolytic cleavage during in vitro manipulations. Calculations of mass, from gel electrophoretograms, for the large and small main ribosomal ribonucleic acid species and for the two chains derived from the large species gave values of 1.37, 0.84, 0.70 and 0.57 X 10(6) daltons, respectively. Sedimentation velocity measurements in sucrose gradients and in the analytical ultracentrifuge indicated sedimentation coefficients of 24 and 18 S for the large and small main species, respectively. Saturation hybridization curves showed that the nuclear genome, quantified by chemical analysis, contains about 114 ribosomal ribonucleic acid gene copies.