Probable component of the triterpene saponins (e.g. ginsenosides) biosynthetic pathway (PubMed:26032089). No detectable activity toward protopanaxatriol (PPT) (PubMed:26032089). (20S)-ginsenoside F1 + UDP-alpha-D-glucose = (20S)-ginsenoside Rg1 + H(+) + UDP Secondary metabolite biosynthesis; terpenoid biosynthesis. Belongs to the UDP-glycosyltransferase family.