SRY-related cDNAs, XLS13A and XLS13B, have been isolated from Xenopus laevis ovary. The cDNAs encode polypeptides of 382 and 375 amino acids, respectively. Nucleotide sequences of the two cDNAs are highly homologous to each other. The type-A and type-B XLS13 proteins, and xSoxl3 reported previously share an identical high mobility group (HMG) box at the amino acid level, although they contain silent nucleotide alterations. The HMG box exhibits strong similarity (> 93% amino acid identity) to those of mouse Sox4/human SOX4 and chicken Sox11/human SOX11. The size of XLS13A/XLS13B mRNA was estimated to be 2.8 knt in Xenopus ovary by Northern analysis. Reverse transcription/polymerase chain reaction (RT/PCR) assay indicated that XLS13A and XLS13B mRNAs are present in various tissues of adult frog. The mRNAs of XLS13A and XLS13B of maternal origin found in unfertilized eggs disappear in the early stages of the Xenopus embryo. DNA-binding properties of the XLS13 HMG domain were examined by electrophoretic mobility shift assay (EMSA). The HMG domain preferentially binds to the canonical target sequence of SOX proteins, AACAAT, in vitro.
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