The function of SEPHS1 (selenophosphate synthetase 1, ENSG00000086475) is as follows. Core component of the zincore complex, a heterotetramer that acts as a molecular 'grip' to stabilize transcription factors at DNA- binding sites across the genome, thereby controlling gene expression (PubMed:40608935). The zincore complex binds specifically to zinc finger transcription factors, such as ZFP91, ZNF652, ZNF526 and PRDM15, and stabilizes them onto their cognate DNA motif (PubMed:40608935). Within the complex, SEPHS1, recognizes and binds the backbone of zinc fingers of transcription factors in a sequence-independent manner via its arginine clamp, enhancing their DNA-binding stability (PubMed:40608935). Plays an essential role in redox homeostasis (PubMed:31607477). May also be involved in selenocysteine biosynthesis by catalyzing formation of selenophosphate from selenide and ATP (PubMed:7665581). Its role in selenocysteine biosynthesis is however unclear and several studies suggest that it does not act as a selenophosphate synthase in vivo or plays an non-essential role (PubMed:15534230). Required for cardiac differentiation (By similarity). {ECO:0000250|UniProtKB:Q8BH69, ECO:0000269|PubMed:15534230, ECO:0000269|PubMed:31607477, ECO:0000269|PubMed:40608935, ECO:0000269|PubMed:7665581}.