Storkhead Box Protein 1 (STOX1)

STOX1 encode 3 different proteins of 989 (isoform A), 227 (isoform B), and 169 (isoform C) amino acids. Isoform A has an 87-amino acid DNA-binding winged helix domain, a nuclear localization signal, and a nuclear export signal. The winged helix domain does not have the characteristic Y/F sequence conserved in the related FOXO protein family. Isoform B lacks the nuclear export signal, and isoform C lacks the nuclear export signal and part of the winged helix domain. Immunolocalization of fluorescence-tagged proteins localized isoform A to either the nucleus or the cytoplasm of transfected immortalized normal diploid extravillus trophoblasts, but no cells showed both nuclear and cytoplasmic fluorescence. Isoform B localized to the nucleus, and isoform C to the nucleolus.