The effect of haemin on RNA synthesis and stability in differentiating rabbit erythroblasts

Haemin accelerates the maturation of erythroid cells but whether this is the result of increased globin gene transcription or processing and stabilization of globin mRNA is not clear. The effect of haemin on the synthesis and stability of non‐globin messengers is also unknown. We examined the changes that occur in RNA metabolism when anaemic rabbit bone marrow erythroblasts, fractionated into immature and mature fractions, are cultured with 20 μM or 50 μM haemin for brief periods (5–8 h). With both cell types haemin increases the incorporation of [ 3 H]uridine into newly synthesized RNA, particularly into the poly(A)‐rich fraction which can increase threefold. Haemin also increases the sythesis of globin mRNA (up to 500 % absolutely and 50 % relative to the synthesis of total RNA) in the immature, but not in the mature, cells. These results suggest that haemin increases the transcription of both globin and non‐globin mRNAs and that the relative increase of each depends on the stage of erythroid cell development. When the [ 3 H]RNA from prelabelled cells was chased in the presence of haemin (with or without actinomycin D) the proportion of 3 H remaining in globin mRNA increased in the immature, but not in the mature, cells. These changes in the relative concentration of globin mRNA were also shown by the translation of extracted bone marrow RNAs in a nuclease‐treated reticulocyte lysate. We conclude that a secondary effect of haemin is on RNA stability and that it enhances the accumulation of globin mRNA by both molecular and cellular mechanisms.