Sulfotransferase involved in dorsoventral axis patterning in early embryos. Required for the specific ventral activation of a series of proteases acting in the perivitelline space between the embryonic membrane and the eggshell. Probably acts by mediating the sulfation of some glycoprotein or glycosaminoglycan stably deposited in the egg, whose ventrally localized modification leads to spatially restricted activation of the protease cascade. Interacts directly with windbeutel (wbl). Wbl is required for its processing into the Golgi. Isoform 4 is ovary-specific. Isoform 4 and isoform 5 are specifically expressed in the ventral follicle cells of the egg chamber. Expressed from stage 12 embryos and continues throughout development. Isoform 4 is expressed from stage 14 in the somatic component of the embryonic ovary. Down-regulated by gurken (grk) and EGF receptor signaling, preventing its expression in dorsal follicle cells. Belongs to the sulfotransferase 3 family. Truncated N-terminus. Truncated N-terminus. Wrong choice of frame. Intron retention. Wrong choice of frame.