Cytologic evidence for increased rRNA gene activity in hemin-induced K562(S) cells.

Hemin-induced K562(S) cells have been studied for the following parameters: cell proliferation, erythroid induction, hemoglobin accumulation, and activation of ribosomal gene clusters 48 hr after hemin induction. Increased transcriptional activity of rRNA genes has been demonstrated by cytochemical methods at both the cell population and single cell level. The following results have been obtained: (a) The vast majority of induced cells shows a highly significant increase in the number of active rRNA gene clusters per cell. At this time, the number of benzidine-positive cells and the quantity of hemoglobin per cell are almost doubled. (b) Specific rRNA gene clusters are activated within single cells. Activation can be visualized at the single gene cluster level. (c) The increase in the average number of active ribosomal gene clusters per cell is not due to clonal selection, but rather to diffuse activation of several gene clusters. (d) The transcriptional activity of rRNA genes has been shown to be regulated at the cellular level by an agent known to specifically induce derepression of genes responsible for erythroid differentiation.