RNA recognition and translational regulation by a homeodomain protein

In Drosophila , the primary determinant of anterior pattern is the gradient morphogen bicoid (bed), a homeodomain protein that binds DMA and transcriptionally activates target genes at different threshold concentrations. Here we present evidence that bed also binds RNA and acts as a translational represser to generate an opposing gradient of the homeodomain protein caudal (cad). RNA binding by bed seems to involve direct interactions between the bed homeodomain and discrete target sequences within the 3′ untranslated region of the cad messenger RNA and to block the initiation of cad translation.