Abstract
The mechanisms controlling the expression of two genes during the differentiation of HL60 cells have been studied. The relative abundance of one mRNA, designated 2B5, increases during retinoic acid-induced differentiation; this increase can be accounted for, in part at least, by a marked increase in the rate of transcription of the gene. The relative abundance of the second, pCG56, decreases during retinoic acid-induced differentiation although the rate of transcription of this gene also increases during the course of differentiation. The bulk of pCG56 transcripts, though polyadenylated and apparently fully processed, are located in the nuclei of the uninduced cells, but on the polysomes of the induced cells. The data indicate that the change in the expression of the gene encoding pCG56 RNA is regulated differently from that encoding 2B5 RNA, and are interpreted as evidence that the pCG56 gene is regulated by an interaction between transcriptional and post-transcriptional controls. Furthermore, the latter includes both mRNA stability and a post-transcriptional mechanism that has not previously been demonstrated in differentiating cells, viz. nucleo-cytoplasmic transport of mRNA.