Control of ribosomal RNA maturation in differentiating yolk sac erythroid cells

Abstract

The processing of nucleolar pre-ribosomal RNA to cytoplasmic ribosomal RNA has been studied in differentiating yolk sac erythroid cells from mouse fetuses at the 10th and 13th day of gestation. The transcription of ribosomal genes is 20 times faster in less differentiated erythroblasts at day 10 than in mature erythroid cells at day 13; conversely, the processing of the methylated portion of 45S RNA is completely conservative in erythroid cells at day 13, but is conservative only at 20% in erythroblasts at day 10. In day-10 erythroblasts the processing of 32S RNA to 28S RNA is inhibited and both 32S RNA and 45S RNA accumulate in nucleoli; at the same time 18S RNA in excess over 28S RNA is destroyed before reaching the stage of mature ribosomes. The inhibition of 32S RNA processing is not due to a deficit of methylation, but may be related to a deficient complementation of proteins to newly made nucleolar RNA.