The erythroid-specific protein encoded by this gene, and the ubiquitous transcription factor CP2, form the stage selector protein (SSP) complex, which is involved in preferential expression of the gamma-globin genes in fetal erythroid cells. Alternate use of an in-frame upstream non-AUG (CUG) translation initiation codon, and a downstream AUG codon, results in two isoforms. While the long isoform (22 kDa) acts as an activator, the short isoform (14 kDa) has been shown to repress gamma-globin gene expression. This gene is located in an intron of the FBXL13 gene on the opposite strand.