Rainbow trout Sox24, a novel member of the Sox family, is a transcriptional regulator during oogenesis.

We isolated a cDNA clone encoding a novel SRY-type HMG box (Sox) protein, designated Sox24, from a rainbow trout ovary cDNA library. On the basis of the HMG box amino acid sequence, Sox24 can be categorized into the same subgroup of Sox proteins as SOX4, SOX11, and SOX22. The proteins in this group also share a highly conserved sequence at the C-terminus. The Sox24 mRNA is expressed at high levels in the ovary, and in-situ hybridization localized its expression to oocytes. The recombinant protein containing the Sox24 HMG box region bound to an AACAAT sequence strongly in a gel retardation assay. Upon co-transfection into CHO cells, the full-length Sox24 transactivated transcription from a reporter plasmid through the AACAAT binding motif. We used GAL4/Sox24 chimeras with the DNA binding domain of yeast GAL4 at the N-terminus to map the transactivation function to the C-terminal region, which included the conserved sequence. These results suggest that Sox24 plays a role as a transcriptional regulator during oogenesis.