Cloning and mapping of Np95 gene which encodes a novel nuclear protein associated with cell proliferation

We previously obtained a monoclonal antibody (Th-10a mAb) that recognizes a single 95-kDa mouse nuclear protein (NP95). Immunostaining analyses reveal ed that the NP95 was specifically stained in the S phase of normal mouse th ymocytes. In contrast, mouse T cell lymphoma cells exhibited a constantly h igh level of NP95 accumulation irrespective of cell stages during the cell cycle. In the present study, we isolated the cDNA encoding the NP95 from a lambda gt-11 cDNA expression library, using the Th-10a mAb. Sequencing of t he whole 3.5-kb cDNA revealed that NP95 is a novel nuclear protein with an open reading frame (ORF) consisting of 782 amino acids. The ORF contains a zinc finger motif, a potential ATP/GTP binding site, a putative cyclin A/E- cdk2 phosphorylation site, and the retinoblastoma protein (RB)binding motif "IXCXE". The chromosomal location of Np95 gene was determined by fluoresce nce in situ hybridization. Np95 gene locates on mouse Chromosome (Chr) 17DE 1.1. and rat Chr 9q11.2-q12.1. Np95 was strongly expressed in the testis, s pleen, thymus, and lung tissues, but not in the brain, liver, or skeletal m uscles. These results collectively implicate this novel nuclear protein in cell cycle progression and/or DNA replication.