We have been investigating the regulation of the human fetal (gamma) and adult (beta) globin genes to identify the transcriptional control signals for these genes. Using transgenic mice we have shown that the transcription of closely linked human gamma and beta globin genes is developmentally regulated, demonstrating that the developmental regulatory sequences are located close to each gene. Recently we have shown that the human beta globin gene acquires DNAse I hypersensitive sites that are concordant with those of the previously uncharacterized mouse adult beta globin genes. In contrast the gamma gene remains relatively hypersensitive throughout development, and independent of the presence of hypersensitive sites in it's two evolutionary homologues in the mouse, betahO and betahl. We are attempting to corroborate our analysis of globin promoter function in K562 cells by demonstrating correctly initiated globin CAT mRNA in transfected cells. We have developed a new CAT gene that contains the 3' RNA processing signals and a set of RNAse protection assay probes to achieve this goal.