A novel initiator/promoter element within the CD45 upstream region

Transcripts of the murine hematopoietic cell surface antigen CD45 (also known as Ly-5, LCA, T200 and B220) initiate at three distinct sites--P1a, P1b and P2--within the upstream region, though P1b is the major site of initiation in lymphoid cells. In our studies of the CD45 upstream region, we identified a cluster of nucleotides comprising the P2 start site, called the TC box, that acts as a minimal promoter for transcription from the P2 site. Thus, the TC box is functionally analogous to elements called initiators that direct RNA polymerases to begin transcription at specific positions. However, in contrast with other initiators, the CD45 TC box directs activated tissue specific expression. The TC initiator, therefore, may provide an effective means to achieve broad expression of exogenously introduced genes in immunologically relevant cells.