Salt-inducible kinase-1 (SIK1) is phosphorylated at Ser577 by protein kinase A in adrenocorticotropic hormone-sti-mulated Y1 cells, and the phospho-SIK1 translocates from the nucleus to the cytoplasm. The phospho-SIK1 is dephosphorylated in the cytoplasmand re-enters thenucleus several hours later. By using green-fluorescent protein-tag-ged SIK1 fragments, we found that a peptide region (586– 612) was responsible for the nuclear localization of SIK1. Theregionwas namedthe RK-rich region because of its Arg- and Lys-rich nature. .
