Absolute rates of globin gene transcription and mRNA formation during differentiation of cultured mouse erythroleukemia cells

We have compared the rates of α- and β-globin gene transcription with the rates of mature globin mRNA appearance in the cytoplasm during the course of chemically induced differentiation of mouse erythroleukemia cells by in vivo pulse-labeling experiments. The absolute rates for both processes were determined by simultaneously measuring incorporation into globin-specific transcripts and into the cellular nucleotide pool. The latter measurements provide a determination of the absolute rate of total RNA synthesis which declines during differentiation. Transcription from the β major and β minor globin genes was measured separately by hybridization to cloned DNA sequences from a region of the second intron which is highly divergent in the two genes. The results show that, during dimethyl sulfoxide-stimulated differentiation, transcription of α and β major globin increases 15-25-fold, whereas β minor globin transcription is not increased. Furthermore, in both undifferentiated and differentiated cells, the absolute rates of globin transcription are about equal to the rate of appearance of mature mRNA transcripts in the cytoplasm, indicating highly efficient processing of nuclear globin transcripts to mature mRNA before and after differentiation. The results indicate that dimethyl sulfoxide-induced accumulation of globin mRNA during differentiation is controlled almost entirely at the transcriptional level.