RNA-BINDING AND TRANSLATIONAL SUPPRESSION BY BICOID

THE anterior determinant bicoid (bcd) of Drosophila is a homeodomain p rotein. It forms an anterior-to-posterior gradient in the embryo and a ctivates, in a concentration-dependent manner, several zygotic segment ation genes during blastoderm formation(1-4). Its posterior counterpar t, the homeodomain transcription factor caudal (cad)(5-7), forms a con centration gradient in the opposite direction, emanating from evenly d istributed messenger RNA in the egg. In embryos lacking bcd activity a s a result of mutation, the cad gradient fails to form and cad becomes evenly distributed throughout the embryo(8). This suggests that bcd m ay act in the region-specific control of cad mRNA translation. Here we report that bcd binds through its homeodomain to cad mRNA in vitro, a nd exerts translational control through a bcd-binding region of cad mR NA.