Structure, expression, and chromosomal localization of human GAK

Abstract

We previously cloned a rat cDNA encoding GAK, an association partner of cyclin G and CDK5. Here, we report the cloning of a cDNA encoding human GAK (1311 amino acids) and show that all of the unique motifs that characterize rat GAK, such as the presence of a Ser/Thr kinase domain, a tensin/auxilin homologous domain, and a Tyr phosphorylation target site, are conserved. The expression profiles of GAK and cyclin G during the synchronized HeLa cell cycle showed that GAK expression oscillates slightly, peaking at G1 phase, although the histone H1 kinase activity remains constant throughout the cell cycle. We also found that the kinase activity of immunoprecipitates of anti-cyclin G antibody fluctuates during the cell cycle with a peak at G1 phase, although the expression level of cyclin G remains almost constant. Northern blot analysis showed that GAK is expressed ubiquitously, with the highest level of expression being observed in the testis. By the FISH technique, we assigned the chromosomal localization of GAK to 4p16.