Sex determining Region of the Y chromosome (SRY) is the Y-borne gene required for male sex determination. Many XY females with complete
gonadal dysgenesis carry SRY mutations. We describe here the effects of eight clinically isolated point mutations on the
DNA-binding and -bending functions of SRY. We found that the seven mutations in the HMG domain affected the
protein's DNA-binding and -bending activities to varying degrees, although all cause complete
gonadal dysgenesis.
DNA binding was abolished by the R75N and L94P mutations, severely disrupted by the F67V mutation and reduced by the M64R (6-fold), R76P (4-fold), A113T (3-fold), and M78T (1.7-fold) mutations. Of these, variant M64R showed no
DNA-bending activity, while M78T caused a mild reduction in
DNA bending. The S18N mutation, a familial mutation that lies outside the HMG domain and caused partial
gonadal dysgenesis in one patient, had minimal effect on
DNA binding and bending. Analysis of the NMR
solution structure of the SRY HMG domain bound to
DNA suggests that mutations disrupt the
protein's conformation (helicity, packing), or interactions at the
DNA interface. The degree to which mutations causing complete
gonadal dysgenesis affect the
DNA-binding activity varies. We propose that there is a threshold level of SRY activity or expression required for testis determination, as we observe that familial mutations have the least effect on SRY activity.