Defective importin beta recognition and nuclear import of the sex-determining factor SRY are associated with XY sex-reversing mutations.
The architectural transcription factor SRY (sex-determining region of the Y chromosome) plays a key role in sex determination as indicated by the fact that mutations in SRY are responsible for XY gonadal dysgenesis in humans. Although many SRY mutations reduce DNA-binding/bending activity, it is not clear how SRY mutations that do not affect interaction with DNA contribute to disease. The SRY high-mobility group domain harbors two nuclear localization signals (NLSs), and here we examine SRY from four XY females with missense mutations in these signals. In all cases, mutant SRY protein is partly localized to the cytoplasm, whereas wild-type SRY is strictly nuclear. Each NLS can independently direct nuclear transport of a carrier protein in vitro and in vivo, with mutations in either affecting the rate and extent of nuclear accumulation. The N-terminal NLS function is independent of the conventional NLS-binding importins (IMPs) and requires unidentified cytoplasmic transport factors, whereas the C-terminal NLS is recognized by IMPbeta. The SRY-R133W mutant shows reduced IMPbeta binding as a direct consequence of the sex-reversing C-terminal NLS mutation. Of the N-terminal NLS mutants examined, SRY-R62G unexpectedly shows a marked reduction in IMPbeta binding, whereas SRY-R75N and SRY-R76P show normal IMPbeta binding, suggesting defects in the IMP-independent pathway. We conclude that SRY normally requires the two distinct NLS-dependent nuclear import pathways to reach sufficient levels in the nucleus for sex determination. This study documents cases of human disease being explained, at a molecular level, by the impaired ability of a protein to accumulate in the nucleus.
Harley
Vincent R
VR
Prince Henry's Institute of Medical Research, Melbourne 3168, Victoria, Australia. vincent.harley@med.monash.edu.au
Layfield
Sharon
S
Mitchell
Claire L
CL
Forwood
Jade K
JK
John
Anna P
AP
Briggs
Lyndall J
LJ
McDowall
Sharon G
SG
Jans
David A
DA
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D012734:Disorders of Sex Development; D005260:Female; D024282:Genes, sry; D006061:Gonadal Dysgenesis, 46,XY / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008297:Male; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D017386:Sequence Homology, Amino Acid; D019849:Sex Determination Processes; D051876:Sex-Determining Region Y Protein; D014157:Transcription Factors; D028961:beta Karyopherins / Q000378:metabolism*
D004268:DNA-Binding Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C497745:SRY protein, human; D051876:Sex-Determining Region Y Protein; D014157:Transcription Factors; D028961:beta Karyopherins; D004247:DNA