The ribonucleic acids of Crithidia fasciculata

Crithidia fasciculata ribosomes were found to be 80S and to dissociate into 58 and 41S subunits; on 5 to 50% sucrose gradients, rRNA was separated into 25, 18, and 5S components. The molecular sizes of the heavier rRNA species, estimated by polyacrylamide gel electrophoresis were 1.24 and 0.84 M (X 10(6) daltons). The 25S RNA has a tendency to interact with the 18S RNA to give a complex that is difficult to separate by sucrose gradient centrifugation. The 25S RNA is also unstable and dissociates into 0.73 and 0.57 M components. The 18S RNA has molecular size (0.84 M) higher than the 0.7 M reported for most eukaryotes, but similar to that of Euglena and Amoeba. Ribosomal RNA hybridized 0.29% of the nuclear DNA. Mitochondrial RNA, extracted by a rapid procedure was resolved into 16 and 5S components in sucrose gradients.