We have been investigating the regulation of the human fetal gamma globin genes to identify the transcriptional control signals for these genes. Among these transcriptional control elements are promoters, enhancer elements and inducible elements which act in cis to a gene, and trans acting factors that presumably control transcription and methylation. Previously we showed that a 750 bp region located 3' to the A gamma gene had many of the properties associated with enhancer elements. We have completed our characterization of this sequence by demonstrating that this sequence increases mRNA transcription, and that it contains tissue specific DNA' se I hypersensitive sites. These findings confirm that this sequence has all of the characteristics commonly associated with enhancer elements. We have also characterize in detail 3 lines of transgenic mice that contain linked human gamma and beta globin genes. We found that these genes were expressed either in the embryonic yolk sac (gamma) and fetal liver (beta) respectively. However, the gamma gene remains hypomethylated in the fetal liver even though it is not expressed, indicating that under methylation is necessary but not sufficient for transcription and that the factors that control transcription and methylation are not identical. Finally, we have analyzed the function of all of the human globin gene promoters in the erythroid cell line K562, and found that short promoters are appropriately expressed, and that changes in the secondary structure of the gamma promoter can cause an increase in transcription.
