Gap protein --> GTPase activating protein
gap may itself be regulated by phospholipids and by phosphorylation on a tyrosine residue by growth factor receptors (pdgf R, egf R). The neurofibromatosis type 1 gene NF1) codes for a protein homologous to gap. Gap has both SH2 and SH3 domains. Another example is sar 1 (from yeast).