This unusual feature of the nucleoplasmin nuclear location sequence suggests ways in which it could interact with the nuclear transport mechanism. The minimal sequence element is therefore necessary but not sufficient for transport into the cell nucleus. The 14-amino acid proposed minimal nuclear location sequence is present in the functional sequences, AVKRPAATKKAGQAKKK, RPAATKKAGQAKKKKLD, and the sequence AVKRPAATKKAGQAKKKKLD, which has additional amino acids at both ends. Restoration of three amino acids of nucleoplasmin sequence at either end of this sequence generated sequences that were able to locate pyruvate kinase to the cell nucleus. When tested directly, however, this sequence was unable to locate pyruvate kinase to the cell nucleus. Deletion analysis was used to determine the limits of a nuclear location sequence and indicated that a 14-amino acid segment (RPAATKKAGQAKKK) should function as a minimal nuclear location sequence. Chapter 7: Describe the experiment that suggested that a particular sequence of amino acids served as a kind of 'zip code' to direct large proteins, such as nucleoplasmin, into the nucleus The pulse chase experiment found that molecules tails that were injected with nuclear localization signals were found in the nucleus while their cores were. Nucleoplasmin is rich in acidic amino acids ( 20 aspartic and glutamic acid), and the phosphorylation that occurs on oocyte maturation makes the protein even more acidic. We show that none of these is able to locate chicken muscle pyruvate kinase to the cell nucleus. Nucleoplasmin is the most abundant protein in the nuclei of Xenopus oocytes representing up to 10 of the total nuclear protein ( Krohne and Franke, 1980 Mills et al. The carboxy-terminal tail of nucleoplasmin, which specifies entry into the cell nucleus, contains four short sequences that are similar to previously identified nuclear location sequences.
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