The homeotic gene Sex Combs Reduced of Drosophila: gene structure and embryonic expression.

The homeotic gene Sex Combs Reduced (Scr) of Drosophila is required during embryogenesis for labial and first thoracic segment development. We define the Scr gene structure, showing that the major embryonic transcript is proximal to the fushi tarazu gene, and report the sequence of the transcript, which encodes a 413-amino acid, homeodomain-containing protein. We describe Scr protein distribution throughout embryogenesis. Expression begins at gastrulation and is eventually apparent in three tissues, epidermis, nervous system and visceral mesoderm, though there are clear contrasts in the domains of expression in these three tissues.