Biochemical defects in eight SRY missense mutations causing XY gonadal dysgenesis

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.