Promoter sequences required for function of the human gamma globin gene in erythroid cells.

The human gamma- and beta-globin genes are expressed during the fetal and adult developmental periods, respectively. Differences in the sequences of their promoters may be relevant to their developmental regulation. The gamma globin gene promoter was found to be stronger than that of the beta gene. In HeLa cells co-transfected with plasmids containing the two genes, transcripts arising from the gamma promoter accumulated to a level 3-fold higher than those initiated from the beta-promoter. We have recently shown that deletion of the most distal of the conserved elements of the promoter (CACCC) reduces function to 25% of the wild-type, whereas the removal of the proximal of the two duplicated (CCAAT) elements increases promoter function 2- to 4-fold in HeLa cells during transient gene expression. Both the wild-type promoter and the truncation and linker-scanning mutants from which one of the two duplicated "CCAAT' elements had been removed, exhibited regulated expression when stably integrated into chromosomes of mouse erythroleukemia (MEL) cells. Thus, duplication of the "CCAAT' element, the feature by which the gamma promoter differs most strikingly from the beta, is not essential for function in erythroid cells.