Characterisation of the nuclear location sequence of Xenopus nucleoplasmin

Each subunit of the Xenopus nucleoplasmin polypeptide possesses a single nuclear location sequence, the boundaries of which have been determined by deletion analysis. However, the sequence identified in this analysis is unable to locate pyruvate kinase to the cell nucleus. Further investigation revealed that while this sequence element is not sufficient for nuclear localisation, it is a necessary feature of slightly longer sequences which can locate pyruvate kinase to the cell nucleus. This unusual feature of the nucleoplasmin sequence suggests testable models for the interaction of this sequence with the transport mechanism, one of which is discussed here.