Dominant and recessive alleles of the Drosophila easter gene are point mutations at conserved sites in the serine protease catalytic domain.

The easter gene, required for the development of all lateral and ventral pattern elements in the Drosophila embryo, appears to encode an extracellular serine protease. Dominant easter alleles increase the number of cells that give rise to lateral and ventral structures. We have found that nine dominant and four recessive mutations are caused by single amino acid substitutions at conserved sites in the putative serine protease catalytic domain. The activity of dominant products was assayed by injecting in vitro synthesized transcripts from the dominant alleles into young embryos. The results suggest that the dominant easter products cleave the normal substrate, but fail to respond to a spatially asymmetric regulator.