A. E. Carrasco, M. Müller, E. M. De Robertis Department of Cell Biology, Biocenter, University of Basel, Switzerland

Drosophila melanogaster is the only organism in which, after 70 years of genetics, genes that control animal development have been identified. Using as a probe a region of homology shared by several Drosophila homeotic genes described by W. McGinnis, W. J. Gehring and colleagues (Nature, 308,428) we cloned from a Xenopus laevis library two DNA segments that hybridize to the Antennapedia, Ultrabithorax and fushi tarazu genes of Drosophila. The frog ‘homeotic domain’ of one gene was sequenced, and it codes for a peptide region of 60 amino acids that is extremely homologous to the fly genes. The frog conserved domain represents an ‘average’ of its three Drosophila counterparts. In other words, if one asks how many of the amino acids are absent from a particular position in any of...

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