FROM SELECTORS TO REALIZATORS

In 1975 Antonio Garcia-Bellido proposed a framework for understanding the morphogenetic function of homeotic genes in terms of selector gene s and realizator genes. Since then, much has been learnt of the molecu lar nature and expression patterns of the Hox selector genes. Our iden tification of realizator genes, and our understanding of how specific sets of realizators are activated in different segments, is still far from complete, however. Here we discuss the nature of the Hox target g enes identified so far and the basis of the target specificity of Hox gene products.