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(696) RFX TRANSCRIPTION FACTORS BIND TO THE PALINDROMIC REGION OF THE HISTONE H1T PROMOTER. Kistler, Malathi1, Horvath, Gary1, Kistler, Stephen1, 1 University of South Carolina, Columbia, SC ABSTRACT- The promoter of the histone H1t gene has attracted attention as a model to study gene expression during spermatogenesis, and our general goal is to use it to identify transcription factors that drive spermatocyte development. While it is closely related to a family of five somatic H1s, H1t expression is restricted to the mid-late pachytene phase of meiosis in the male. On the one hand the promoter shares 4 regulatory motifs with several other H1 genes: an H1-specific AC box, a GC box, a CCAAT element, and TATA box. On the other, it has been shown to have several unique regulatory sites including a palindromic region between the GC box and CCAAT sites, and an inhibitory region between the TATA box and Cap site. RFX transcription factors comprise a family with a conserved winged helix DNA binding domain. They were originally identified as binding to the X box of promoters for major histocompatibility complex class II genes but the family now includes proteins with functions outside the immune system. Northern blots have previously shown that two members, RFX2 & 3, are significantly upregulated in the testis as a whole though cellular locations were not established. Here we show that RFX proteins present in rat testis nuclear extracts bind to the H1t promoter palindromic region and have shown using specific antibodies that complexes are formed from both RFX1 and RFX2. Immunohistochemistry on mouse testis sections showed that RFX2 is markedly upregulated during meiosis at the same time that H1t expression occurs. By contrast, RFX1 reactivity is low in cells expressing H1t. Using oligonucleotide probes and gel mobility shift assays we have shown that RFX binding sites occur in the promoter regions of at least two other genes expressed selectively during meiosis. Accordingly RFX factors may play a critical role in spermatocyte gene expression. Supported by NIH grant HD10793 KEY WORDS: gene expression, transcription factors, meiosis, promoter analysis |
