Changes in p53 mRNA expression during terminal differentiation of murine erythroleukemia cells

The protein p53 is functionally implicated in the normal regulation of cell proliferation. We have previously reported that the rate of p53 protein synthesis is reduced during the cessation of cellular proliferation which accompanies the in vitro induced differentiation of Friend-erythroleukemia cells. In this work we followed the p53 mRNA expression during the differentiation of these cells. We report on a new type of p53 mRNA with a slower electrophoretic mobility on gels, which appeared in the cytoplasmic fraction of the erythroleukemia cells between 1 to 3 days following induction of differentiation and persisted in the cells until Day 7. The larger type of p53 mRNA was found associated with polysomes, suggesting that it is translatable in cells. The difference in size between the noninduced and the differentiation-specific type of p53 mRNAs (about 200 nucleotides) was not abrogated following the deadenylation of the mRNAs, thus excluding the possibility that the altered size might result from a longer poly(A) tract. S1 nuclease mapping of the 3' termini of the p53 mRNAs revealed that the 3' ends of both p53 mRNA types were identical, suggesting that either alternative splicing or a longer 5' noncoding region could cause this heterogeneity in p53 mRNA transcripts.