There are dramatic changes in the basic nuclear proteins that bind to DNA during spermatogenesis. In Mammals the testis-enriched and testis-specific histone variant genes are expressed at high levels in germinal cells. In this paper we review some of the progress made concerning our understanding of the mechanisms involved in regulating expression of the testis histone genes. We examine the tests-specific histone H1t gene in detail and review the evidence that the expression of this gene is regulated primarily at the level of transcription. An 18 bp DNA sequence within the proximal promoter of H1t binds tightly and specifically to testis nuclear proteins in electrophoretic mobility shift assays. UV-crosslinging experiments indicate that testis nuclear proteins form a complex upon binding to the sequence element. This same conserved DNA sequence element is found in all mammalian H1t promoters examined including human, rhesus monkey, and rat. Methylation interference assays reveal that several bases within the conserved core palindromic sequence CCTAGG appear to be important for binding.
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