Transcription Specific repression

Chen X, Bicker JJ (2004) Stage-specific repression by the EKLF transcriptional activator. Mol Cell Biol 24(23) 10416-10424... 

Direct repressors interact with the basal components of the transcription apparatus or with transcriptional activators to inhibit their activity. Specific repressors, analogous to transcriptional activators, are constructed modularly, with a DNA-binding domain and a repressor domain. The repressive character of such domains has been proven in domain swapping experiments. The mechanism of specific repression remains speculative. The following mechanisms are, however, conceivable ... 

The D vitamins are a group of sterols that have a hormone-like funciion. The active molecule, 1,25-dihydroxycholecalciferol (1,25 diOH D3), binds to intracellular receptor proteins. The 1,25-diOH D3-receptor complex interacts with DNA in the nucleus of target cells in a manner simiar to that of vitamin A (see Figure 28.20), and either selectively stimulates gene expression, or specifically represses gene transcription. The most prominent actions of 1,25-diOH D3 are to regulate the plasma levels of calcium and phosphorus. 

Mack, D. H., J. Vartikar, J. M. Pipas, and L. A. Laimins, Specific repression of TATA-mediated but not initiator-mediated transcription by wild-type p53. Nature 363 281-283, 1993. The p53 protein may repress the activity of certain promoters by direct interaction with TATA box-dependent transcription machinery. 

Selective gene transcription in eukaryotes seems to rely more heavily on the specificity of the template sequences themselves rather than on the specificity of RNA polymerases. RNA polymerase specificity seems to be relatively restricted to the recognition of some specific nucleotide sequence or resulting structural arrangement which constitutes an initiation site on the DNA template of the chromosome. RNA transcription proceeds on those cistrons which are not repressed either by the proteins of the heterochromatin of the chromosome or by structural inhibition. This idea is supported by the demonstration of apparent transcriptional specificity in vitro of chromatin using bacterial RNA polymerase as the transcriptive agent (Paul and Gilmour, 1968 Smith et ah, 1969 Paul, 1970). 

Muliprotein complexes that do not directly bind DNA, but are recruited by sequence-specific transcription factors and mediate their capacity to activate genes (coactivators) and to repress genes (corepressors). 

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