Characterization of an unique RNA initiated immediately upstream from human alpha 1 globin gene in vivo and in vitro: polymerase II-dependence, tissue specificity, and subcellular location.

We have identified an abundant transcript initiated upstream from the canonical cap site of human alpha 1 globin gene in bone marrow cells and in COS-7 cells transfected with an alpha 1 globin gene-containing plasmid. Similar to the major alpha 1 globin transcript, this upstream RNA is present almost exclusively in the cytoplasm of the transfected COS-7 cells. It is also synthesized efficiently in vitro by RNA polymerase II in the nuclear extracts prepared from a Hela cell line and an erythroleukemia cell line, K562. RNAs isolated from these cell lines, however, do not contain this upstream transcript. The putative 5' end of the alpha 1 globin upstream RNA is mapped by primer extension to base -45, which is located in between the CCAAT and TATA boxes. The synthesis of this RNA in vitro and in vivo, and the close proximity of its 5' end to the promoter of the alpha 1 globin gene suggest a common mechanism regulating the transcriptional initiation of both the upstream and the major alpha 1 globin RNAs.