Transcriptional regulation in avian erythroid cells

Both the translational and transcriptional repertoires of nearly mature avian erythroid cells appear to be highly restricted: molecular hybridization experiments demonstrate the presence of about 4000 species of poly(A)+ nRNA and fewer than 100 species of poly(A)+ mRNA. This paper addresses the question of whether the nRNA of erythroid cells contains sequences which, although not expressed in the erythroid cells, are found on polysomes in another cell type. We have prepared cDNA from liver mRNA and have determined the representation of liver mRNA sequences in the erythroid cell nRNA. Liver mRNA consists of about 14 000 species of poly(A)+ RNA. Of these only about 100 species are detectable in erythroid cell nRNA. The vast majority of liver mRNA species is undetectable in erythroid cells; i.e., they are present at less than 0.03 copies per cell. The few species of liver mRNA that are detectable in erythroid cells are present in both the nuclear and polysomal RNA at concentrations less than 0.1 copies per cell. These data suggest that gene expression in avian erythroid cells is highly regulated at the transcriptional level.