A TESTIS-SPECIFIC GENE ENCODING A NUCLEAR HIGH-MOBILITY-GROUP BOX PROTEIN LOCATED IN ELONGATING SPERMATIDS

A cDNA encoding a DNA-binding protein has been isolated by screening a mouse testicular expression cDNA library with a concatemer of a 12-bp putative protein-binding element present in the promoter of the testi s-specific gene PGK-2. Sequence analysis of the isolated cDNA indicate d the presence of an open reading frame that encodes a protein with tw o conserved DNA-binding motifs known as the high-mobility-group (HMG) boxes. Northern (RNA) blot analysis demonstrated that expression of th e gene is restricted to the postpuberal testis. The DNA-binding activi ty and sequence specificity of the recombinant HMG protein were confir med by DNA mobility shift assay using the initial concatemer of the PG K-2 promoter element as a probe as well as the wild-type or mutated ve rsions of the 12-bp element within its natural sequence context. Immun ocytochemical staining of adult testis sections with polyclonal antise ra recognizing this recombinant HMG protein demonstrated that it is lo cated predominantly in the nuclei of elongated spermatids at steps 9 a nd 10. These results suggest that this novel HMG box protein gene may be involved in the regulation of gene expression of the haploid male g enome. The gene from which the cDNA was derived has been termed testis -specific HMG (tsHMG).