Comparative HMG-box sequences of the SRY gene between sheep, cattle and goats.

In mammals, sexual differentiation of the gonads during development depends on the presence of the Y chromosome (1). The testis-determining gene lies on the Y chromosome, and has been delimited in human to a 35-kilobase region near the pseudoautosomal boundary (2). SRY is a gene located in this region and both conserved during evolution and Y chromosome specific in a number of mammals (3). The predicted amino acid sequence of SRY contains a domain characterized by a homology with hUBF (4), the Me protein of the fission yeast Schizosaccharomyces pombe (5), the high-mobility-group protein HMG] (6) and the lymphoid-specific enhancer binding factor LEF-1 (7). This domain of 70-residues termed HMG box is characteristic of DNA-binding proteins. This conserved motif represents a functional protein domain necessary for DNAbinding activity of SRY. Until now, all mutations in the SRY gene associated with sex inversion have been located within the HMG box (8, 9). Using oligonucleotide primers (5' end: 5'-TGAAGCGACCCATGAACG-3'; 3' end: 5'-CGACGAGGTCGATACTTA-3') within the HMG box in the human SRY sequence, genomic DNA from males and females of the Bovidae family was amplified by the polymerase chain reaction (PCR). The resulting male specific amplified fragments were sequenced after assymetric PCR. The 200 bases pairs of the sequence of each PCR product have been determined and are presented in Figure 1. The nucleic acid comparison reveal a very high degree of conservation of the SRY-HMG box within the Bovidae family. Between the three subfamily (Ovinae, Bovinae, Caprinae) more than 97% of homology is observed. Concerning the amino-acids predicted sequences, the homology is total between the sheep and the goat and three residues are different in the cattle HMG-box region of the SRY gene (Figure 2). Based on this data a mammalian consensus sequence including human, mouse, rabbit and marsupials sequences can be established. Amino-acids present throughout all known mammalian SRY genes could be identified from the consensus sequence. These critical residues probably implicated in the DNA binding activity seem to be require to mediate the action of SRY in sex determination.