MOLT - l 3 KG - la U 937 THP - 1 A 3 . 01 Raji P - Actin CD 34 ( exons

The human CD34 surface antigen is selectively expressed on stemlprogenitor cells within the hematopoietic system. Because CD34 expression is tightly linked to the immature status of hematopoietic cells, with expression being rapidly lost as hematopoietic cells mature and differentiate, an examination of its regulation may provide important insights into the molecular control of blood cell development. A eomparison of the CD34 nuclear transcription rate in CD34+ and CD34cells indicated that the CD34 gene is transcriptionally regulated in hematopoietic cell lines. In a previous report, we had identified two major clusters of CD34 transcription initiation sites by 5' RACE (rapid amplification of cDNA ends) analysis. In transient transfection experiments, we now demonstrate the ability of sequences encompassing each of these clusters to function as promoters of transcription in CD34' cells. These promoters functioned at equivalent lev-