We reported previously that mouse ING1 homolog (mINGh), localized in the nucleus, enhanced cell death in HC11 mouse mammary epithelial cells. Analysis of the mINGh amino acid sequences revealed the presence of potential nuclear localization signal (NLS) and plant homeodomain (PHD) finger DNA binding domain. In the present study, NLS site in mINGh was determined using different pieces of mutant mINGh proteins. which were fused to green fluorescent protein (GFP), and transfected into HC11 cells. NLS of mINGh was split into two parts consisting of amino acids KEKK and KKLK. Mutation in NLS sites of mINGh resulted in no enhancement of the cell death when over-expressed. These results indicated that mINGh contains NLS of bipartite type, which is essential for the regulation of cell death. (C) 2002 Elsevier Science (USA). All rights reserved.