PSG1 belongs to a subgroup of transcription factors that are phosphorylated upon binding to promoter sequences. PSGs are part of the carcinoembryonic antigen (CEA) family and serve as early biochemical markers of syncytiotrophoblast formation. The sequence specificity of DNA binding is conferred by Zn (II) fingers, whereas a different region of PSG1 appears to regulate the affinity of DNA binding. Additionally, PSG1 is believed to mediate placental vascular morphogenesis by enhancing VEGF-A production and endothelial tube formation. Recombinant human PSG1 protein, fused to His-tag at N-terminus, was expressed in E.coli.