SPOT-1, A NOVEL NLS-BINDING PROTEIN THAT INTERACTS WITH P53 THROUGH ADOMAIN ENCODED BY P(CA)(N) REPEATS

Nuclear Localization Signals (NLS) have been found to mediate the impo rt of proteins into the nucleus. Proteins interacting directly with NL S control the subcellular localization of nucleophillic proteins. The p53 protein is spatially regulated throughout the cell cycle and this regulation has been shown to be dependent on the presence of its NLS s equences. We identified three novel cDNA clones that were isolated fro m an expression library because they encode polypeptides that bind a s ynthetic peptide containing the major NLS of p53 (NLS I). These clones were found to share a common domain encoded by p(CA)(n) repeats; a si mple sequence length polymorphism (SSLP). This is the first report whe re p(CA)(n) repeats mere found to encode protein. One cDNA clone encod es a fun length, 16 kDa protein, designated spot-1, that is represente d in cells predominantly as oligomers. spot-1 interacts with the NLS I of p53 through its p(CA)(n) repeat. Cell fractionation and immunofluo rescence analysis demonstrated that spot-1 is a nuclear protein which, in fibroblasts, co-localizes with p53.