Nuclear localization signals in the Xenopus FGF embryonic early response 1 protein.
Xenopus early response 1 (XER1) is a fibroblast growth factor-inducible transcription factor whose developmentally regulated nuclear localization is thought to be important in the control of cell differentation during embryonic development [Luchman et al., Mech. Dev. 80 (1999) 111-114]. Analysis of the XER1 amino acid sequence revealed four regions which contain potential nuclear localization sequences (NLSs). Using mutant XER1 proteins and portions of XER1 fused to green fluorescent protein (GFP) transfected into NIH 3T3 cells, we have determined that only one of these, NLS4, located near the carboxy-terminus of XER1, is necessary and sufficient for targeting exclusively to the nucleus. Of the other three predicted NLS sequences, only NLS1, consisting of the sequence (138)RPRRCK(143) was shown to function as a cryptic, weak NLS. NLS4 contains a core region consisting of the sequence (463)RPIKRQRMD(471) which is similar to the core NLS directing the human c-MYC protein to the nucleus. The core sequence is flanked by a predicted cdc2/protein kinase A phosphorylation motif, however mutation of the serine(472) to alanine or aspartic acid had no detectable effect on accumulation of GFP-XER1 fusion proteins in the nucleus, demonstrating that this putative phosphorylation site plays no role in regulating nuclear transport.
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Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, 300 Prince Phillip Drive, St. John's, NF, Canada
Gillespie
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D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D016203:CDC2 Protein Kinase / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D018076:DNA, Complementary; D005346:Fibroblast Growth Factors; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
D018076:DNA, Complementary; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D005346:Fibroblast Growth Factors; D017868:Cyclic AMP-Dependent Protein Kinases; D016203:CDC2 Protein Kinase