GAK is a member of the protein kinase superfamily and the Ser/Thr protein kinase family, with the enzyme classification EC 2.7.11.1. It associates with cyclin G and with CDK5. UniProt annotation indicates that it seems to act as an auxilin homologue involved in the uncoating of clathrin-coated vesicles by Hsc70 in non-neuronal cells. It may therefore play a role in clathrin-mediated endocytosis and intracellular trafficking, and in the dynamics of clathrin assembly and disassembly.

The GAK protein is found in the perinuclear region of the cytoplasm, in the trans-Golgi network, at focal adhesions and in clathrin-coated vesicles. Its expression oscillates slightly during the cell cycle, peaking at G1. The mouse and rat orthologues are both named Gak. Alternative splicing of the GAK gene results in multiple transcript variants encoding different isoforms.

The name reflects its link to cell cycle control. Cell cycle progression is governed by cyclin-dependent kinases, whose activities are regulated by cyclins and CDK inhibitors through phosphorylation and dephosphorylation. Cyclin G is a direct transcriptional target of the p53 tumour suppressor and so functions downstream of p53. GAK is an association partner of cyclin G and CDK5. HGNC places it in the DNAJ (HSP40) heat shock protein group, the C2 tensin-type domain containing group and the Numb-associated kinase family, and lists DNAJC26 as an alias.