The GC-box is critical for high level expression of the testis-specific Hsp70.2/Hst70 gene.

The Hsp70.2/Hst70 gene, which belongs to the 70 kDa heat-shock protein (HSP) family, is expressed specifically in primary spermatocytes and spermatids. The regulatory elements required for a high level of testis-specific expression of the gene are placed between the two major transcription start sites T1 and T2 (approximately 350 and 115 bp upstream of the starting ATG codon). Here we have shown that sequences proximal to the exon1/intron splicing site in the 5' untranslated region of the Hsp70.2/Hst70 gene, which include a highly conserved element called box B, are required for efficient expression of the chloramphenicol acetyltransferase reporter gene in testes of transgenic mice. However, in spite of the drastically reduced overall activity, the stage-specific expression pattern of the transgene was preserved after removal of these sequences. We have also shown that GC-box located downstream of the box B (approximately 210 bp upstream of the starting ATG codon) is indispensable for efficient expression of the Hsp70.2/Hst70 gene promoter in spermatogenic cells. The GC-box specifically binds proteins present in nuclear extracts from testes (putatively Sp1-like factors). A change in the pattern of such GC-box-interacting factors corresponds to activation of the Hsp70.2/Hst70 gene, confirming the importance of this regulatory element.