Transcriptional and translational analysis of the human theta globin gene

The human theta-globin gene in man appears to be functional, based on its sequence and evolutionary conservation. However its physiological role is unknown and furthermore its deletion in some individuals appears to have no effect on erythroid development. We have therefore analysed the transcriptional and translational competence of the theta globin gene to assess whether or not it is a silent or active globin gene. First, we demonstrate that theta globin mRNA is correctly spliced, by sequencing its cDNA. Second, using this theta cDNA, we generated synthetic theta globin mRNA and were able to demonstrate that this mRNA is translated into theta globin protein in wheat germ in vitro translation extracts. Similarly, the theta globin gene transfected into an erythroid cell line produces a protein product that comigrates with theta globin. Finally, we analysed the unusual promoter of the theta globin gene. The GC rich sequence directly adjacent to the multiple cap sites of theta globin mRNA functions as a promoter element in both erythroid and non-erythroid cell lines, while the more usual CCAAT and ATA box regions (found in all other globin genes) which are displaced by the GC rich promoter sequence, do not possess detectible promoter activity. Taken together, these results suggest that theta globin may have some as yet undetermined role in human erythropoiesis.