The resulting fly would have two fronts and no back. Saxophone, along with Thick veins and Punt , constitute the Drosophila receptor for decapentaplegic . These receptors mediate the transduction of DPP signals into the cell. Mutations in these genes have the same effect as mutation in dpp , since without DPP's receptors, its signals fail to be communicated to the cells that should receive them. Saxophone has an intracellular kinase domain and a conserved extracellular cysteine reside structure.
Kinases add phosphate resides to target proteins.
Along with Thickveins, SAX is homologous to type I TGF-beta receptors. Evidence is presented that the concentration of the type I receptor Tkv must be low to allow long-range Dpp diffusion. However, low Tkv receptor concentrations result in low signaling activity. The phenotypic consequences of overexpressing constitutively active forms of Tkv and Sax receptors in the developing wing was investigated using the GAL4-UAS system. When Dpp is ubiquitously expressed in wing discs, they become overgrown and the expression of both Sal and Omb is expanded.