The HMG box family is functionally diverse, with members involved in DNA recognition during nucleosome assembly, recombination and transcription (1 for review). A subclass of these proteins having a single HMG box are likely to be transcription factors and include the mammalian testis deteimnining factor (SRY), T-cell factor (TCF- 1), lymphoid enhancer factor (LEF-l or TCF-lIa) and the yeast sterility factor (Ste I 1); these proteins recognise not only non-B-DNA structures but also specific DNA sequences whose consensus is (A/T)(A/T)CAAA- G (2 for review). Recombinant SRY can bind these DNA sites in a sequence-dependent manner, and this activity is required for testis development (3,6). DNA binding sites for SRY have been deduced from the target sequences of related genes e.g. TCF-1 (3,4), LEF-1 (5), IRE-ABP (6) or from promoter regions of candidate downstream genes e.g. AMH and aromtiatase (7.8). but it remains to be determined whether these are optimal sites for interaction with SRY.