[Maturing of ribosomal RNAs in rat thymus cells]

The peculiarities of maturing of ribosomal RNAs in rat thymus cells were studied. It was found that the rRNA precursors (45s, 41s and 32s) are weakly extractable from the thymocytes at 45 degrees and are predominantly accumulated in the RNA 650 fraction. It was also shown that part of newly synthesized molecules of 18s RNA are broken down in the course of processing. The data obtained confirm the previously made assumption that degradation of some rRNAs in the course of maturing represents a mechanism of maintenance of a constant number of ribosomes in the cell.