RNA binding and translational suppression by bicoid.

The anterior determinant bicoid (bcd) of Drosophila is a homeodomain protein. It forms an anterior-to-posterior gradient in the embryo and activates, in a concentration-dependent manner, several zygotic segmentation genes during blastoderm formation. Its posterior counterpart, the homeodomain transcription factor caudal (cad), forms a concentration gradient in the opposite direction, emanating from evenly distributed messenger RNA in the egg. In embryos lacking bcd activity as a result of mutation, the cad gradient fails to form and cad becomes evenly distributed throughout the embryo. This suggests that bcd may act in the region-specific control of cad mRNA translation. Here we report that bcd binds through its homeodomain to cad mRNA in vitro, and exerts translational control through a bcd-binding region of cad mRNA.