Cyclin G-associated kinase (GAK) harbors a consensus phosphorylation motif (Y412) for c-Src; however， its physiological significance remains elusive. Here， we show that GAK is phosphorylated by c-Src not only at Y412 but also at Y1149. An anti-GAK-pY412 antibody recognized the shifted band of GAK during M phase. Immunofluorescence (IF) showed that GAK-pY412/pY1149 signals were present in the nucleus during interphase， translocated to chromosomes at prophase and prometaphase， moved to centrosomes at metaphase， and finally translocated to chromosomes at the end of telophase， when nuclear membrane formation was almost complete. These subcellular movements of GAK resemble those of DNA licensing factors.... More
Cyclin G-associated kinase (GAK) harbors a consensus phosphorylation motif (Y412) for c-Src; however， its physiological significance remains elusive. Here， we show that GAK is phosphorylated by c-Src not only at Y412 but also at Y1149. An anti-GAK-pY412 antibody recognized the shifted band of GAK during M phase. Immunofluorescence (IF) showed that GAK-pY412/pY1149 signals were present in the nucleus during interphase， translocated to chromosomes at prophase and prometaphase， moved to centrosomes at metaphase， and finally translocated to chromosomes at the end of telophase， when nuclear membrane formation was almost complete. These subcellular movements of GAK resemble those of DNA licensing factors. Indeed， mass spectrometry identified mini-chromosome maintenance (MCM) 3， an essential component of the DNA licensing system， as one of the association partners of GAK; immunoprecipitation-mediated Western blotting confirmed their association in vivo. These results suggest that the c-Src_GAK_MCM axis plays an important role in cell cycle progression through control of the DNA replication licensing system.
