Functions as part of the SSP (stage selector protein) complex, a complex that contributes to the preferential expression of the gamma-gene in fetal erythroid cells by facilitating the interaction of the gamma-globin genes with enhancer elements contained in the locus control region (LCR). The complex binds to the stage selector element (SSE) in the proximal gamma-globin promoter. In contrast, isoform 2 acts as a repressor of gamma-globin gene expression by preventing NFE2 and RNA polymerase II recruitment to the promoter. {ECO:0000269|PubMed:11003662, ECO:0000269|PubMed:15084587, ECO:0000269|PubMed:16263792}. This is the function of NFE4 (nuclear factor, erythroid 4, ENSG00000230257).