TI - Assay and functional properties of the tyrosine kinase Pyk2 in regulation of Arf1 through ASAP1 phosphorylation . AB -The Arf-GTPase-activating protein ( GAP ) ASAP1 has been identified in a yeast-two - hybrid screen as a prominent binder of the proline-rich tyrosine kinase 2 ( Pyk2 ) via SH3 domain -mediated interaction . Following binding , Pyk2 directly phosphorylates ASAP1 on tyrosine residues 308 and 782 in vitro and in cells . To understand the functional impact of this interaction and subsequent phosphorylation , nonphosphorylated and Pyk2 -phosphorylated ASAP1 have been generated . This material can be used for lipid - protein overlay assays and fluorimetric Arf-GTPase tests to show that the Pyk2 -mediated tyrosine phosphorylation of ASAP1 modulates its GAP activity towards Arf1 in vitro . These studies provide the first evidence for a regulation of ASAP1 and hence Arf1 activity by tyrosine phosphorylation and suggest a functional link between tyrosine kinases and Arf GTPases . Furthermore , an assay to study cellular Arf activation and thus GAP as well as guanine nucleotide exchange factor ( GEF ) activities and their regulation is described .