Activation of the Erythropoietin Gene Due to the Proximity of an Expressed Gene

The erythroleukemic cell line IW32 has a normal erythropoietin (epo) gene and one which has undergone rearrangement and amplification. The rearranged epo locus consists of a breakpoint approximately 1 kb upstream from an otherwise structurally unchanged epo gene. DNase I hypersensitivity studies had suggested that the rearranged gene is the transcriptionally active one. To understand this transcriptional activation more fully we have sequenced the upstream regions of both the normal and the rearranged epo genes, the latter encompassing the rearrangement breakpoint. Sequence analysis showed that the new sequence past the breakpoint at the rearranged locus contained all the promoter components needed for a gene in opposite transcriptional orientation to the epo gene. Subsequent Northern blot analysis showed that this gene is transcriptionally active. No homology was found between this gene and any sequence in the data banks. It appears that the transcriptional activation of the rearranged epo gene in IW32 cells has been mediated by a translocation event which has served to bring the epo gene into close juxtaposition to this transcriptionally active gene.