The High Mobility Group Box Transcription Factor Nhp6Ap enters the nucleus by a calmodulin-dependent, Ran-independent pathway.
A gradient of Ran.GTP typically regulates traffic through the nuclear pore by modulating association of receptors with cargo. However, here we demonstrate that the yeast high mobility group box transcription factor Nhp6Ap enters the nucleus via a novel nuclear localization signal recognized by calcium calmodulin in a process that does not require Ran. Calmodulin is strictly required for the nondiffusional nuclear entry of Nhp6Ap. Calmodulin and DNA exhibit mutually exclusive binding to NHP6A, indicating that the directionality of Nhp6Ap nuclear accumulation may be driven by DNA-dependent dissociation of calmodulin. Our findings demonstrate that calmodulin can serve as a molecular switch triggering nuclear entry with subsequent dissociation of calmodulin binding upon interaction of cargo with chromatin. This pathway appears to be evolutionarily conserved; mammalian high mobility group box transcription factors often have two nuclear localization signals: one a classical Ran-dependent signal and a second that binds calmodulin. The finding that Nhp6Ap nuclear entry requires calmodulin but not Ran indicates that Nhp6Ap is a good model for studying this poorly understood but evolutionarily conserved calmodulin-dependent nuclear import pathway.
Hanover
John A
JA
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851.
Love
Dona C
DC
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851.
DeAngelis
Nikki
N
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851.
O'Kane
Meghan E
ME
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851.
Lima-Miranda
Raquel
R
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851.
Schulz
Timothy
T
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851.
Yen
Yi-Meng
YM
Department of Biological Chemistry, UCLA Medical School, Los Angeles, California 90095-1737.
Johnson
Reid C
RC
Department of Biological Chemistry, UCLA Medical School, Los Angeles, California 90095-1737.
Prinz
William A
WA
Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0851. Electronic address: wprinz@helix.nih.gov.
D021581:Active Transport, Cell Nucleus; D000818:Animals; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002417:Cattle; D002843:Chromatin / Q000378:metabolism; D017124:Conserved Sequence; D004247:DNA / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry*; D004926:Escherichia coli / Q000378:metabolism; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000737:chemistry; D024001:HMGN Proteins; D008954:Models, Biological; D008968:Molecular Conformation; D009687:Nuclear Proteins / Q000737:chemistry*; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*; D014158:Transcription, Genetic; D020931:ran GTP-Binding Protein / Q000378:metabolism*
D002147:Calmodulin; D002843:Chromatin; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D024001:HMGN Proteins; C086471:NHP6A protein, S cerevisiae; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D004247:DNA; D020931:ran GTP-Binding Protein