Tissue-specific protein-DNA interactions of the mouse protamine 2 gene promoter

During spermiogenesis, the haploid phase of spermatogenesis, the genome is packaged into a highly compacted form and this process requires replacement of histones by protamines. In the mouse, protamines are encoded by two genes, which are transcriptionally regulated in testis. To understand the regulation of transcription of the mouse protamine 2 (mP2) gene, the tissue-distribution of sequence-specific interactions between nuclear proteins and promoter DNA sequences have been analyzed. Protein binding to the promoter region from -370 to +65 was studied using DNase I footprinting and gel shift assays. Five protein binding sites were identified, which are recognized by nuclear proteins from either testis or liver. Site 1 from -64 to -48, contains part of a cAMP responsive element (CRE), which in testis is recognized by CREM tau, an activator of post-meiotic transcription. Testicular protein(s) also binds to three other promoter domains: site 2, -87 to -67, a region containing a CAAT box, and sites 4 and 5, -239 to -210 and -328 to -311, sequences with similarity to consensus steroid hormone responsive elements (HRE). In contrast, interactions between the mP2 promoter and nuclear factors from liver, a tissue in which the mP2 gene is not transcribed, are observed at sites 1, 2, and 4, as well as at an additional region at site 3, -202 to -175. Because occupancy at site 3 appears to correlate with inactivation of the gene in non-testicular tissues, whereas testicular protein binding at site 5 appears to be associated with active transcription, we conclude that the mP2 promoter displays intricate tissue-specific patterns of protein/DNA interactions at key regulatory elements.