Sax, or Saxophone, is a serine/threonine receptor kinase in Drosophila melanogaster. Other aliases include: Bkr43E; Brk43E; CG1891; Dmel\CG1891; Sa; Sax; SAX; STK-B. It is a member of the protein kinase superfamily. It 570 amino acids long and has a mass of 64.2 kDa.