Characterization of ribonucleoprotein particles from the protozoa Astasia longa.

Ribonucleoprotein particles released from nucleoli of Astasia longa by treatment with heparin were characterized biochemically. When centrifuged in a sucrose gradient containing an appropriate buffer (Tris/KCl/Mg2+), four populations of particles were obtained, sedimenting at 90 S, 75 S, 60 C, and 44 S, respectively. The first type of particles contained the high molecular weight (3.5-10(6) ribosomal RNA precursor. The RNAs present as the major components in the 75-S and 44-S particles had molecular weights of 1.35-10(6) and 0.85-10(6), respectively, whereas the 60-S particles contained a mixture of 0.85-10(6) and 1.35-10(6) RNA. After a brief labeling, the radioactivity was found in the RNA constituent of the 90-S particles; following a 90 min chase, the label disappeared from this latter fraction and accumulated in the 75-S, 60-S and 44-S particles. This indicates a precursor-product relationship between the RNA of the 90-S particles and that of the three other ribonucleoprotein particles, consistent with the conversion:: 3.5-10(6) RNA LEADS TO 1.35-10(6) RNA+0.85-10(6) RNA.