Basal level of transcription

The sequences of eukaryotic promoters are more variable than their prokaryotic counterparts (see Fig. 26-8). The three eukaryotic RNA polymerases usually require an array of general transcription factors in order to bind to a promoter. Yet, as with prokaryotic gene expression, the basal level of transcription is determined by the effect of promoter sequences on the function of RNA polymerase and its associated transcription factors. 

Despite this elaborate binding complex, repression is not absolute. Binding of the Lac repressor reduces the rate of transcription initiation by a factor of 10s. If the 02 and 03 sites are eliminated by deletion or mutation, the binding of repressor to CL alone reduces transcription by a factor of about 102. Even in the repressed state, each cell has a few molecules of /3-galactosidase and galactoside permease, presumably synthesized on the rare occasions when the repressor transiently dissociates from the operators. This basal level of transcription is essential to operon regulation. 

The TATA binding protein and general transcription initiation factors. A slow basal level of transcription can be observed when all but a small part of the control region at the 5 end of a gene is deleted.325 This minimum promoter, which includes the TATA sequence, is the binding site of both the RNA... 

Bacteria, gut micToflora, 142, 143, 147-150 Bactemdes, 14 , 149 Banana, starch content, 139 BarorEceptor , 712 Basal level of transcription, 5 5 Basal metabolic rate (BMR), 302, 735-736 BCAA aminotransferase, 209, 430,433,434, 343... 

The hormonal forms of vitamin A are all-frans-retinoic acid and 9-cfs-retinoic acid. The hormonal form of vitamin D is 1,25-dihydroxyvitamin D3, and that of thyroid hormone is T3. These hormones act within the nucleus, where they bind to special proteins. These proteins are classed as transcription factors. Various transcription factors bind to the regulatory regions of all genes and influence the rate of transcription (Figure 9.60). Many genes are continuously transcribed, and here the term "basal level of transcription" is used to describe the rate of transcription. In cases where the gene is regulated, special transcription factors are used to enhance or inhibit the basal level of transcription. 

The second system is composed of the RolR regulator and the PAS promoter fused with the operator (rolO) from the Corynebacterium glutamicum resorcinol catabolic operon. This promoter has the low basal level of transcription and can be induced by resorcinol. In summary, there are significant numbers of well-characterized synthetic and inducible promoters to control the expression of gene and gene clusters in streptomycetes [81]. 

The presence of a very low level of the 0.3 kb transcript in high CO2 cells suggests that there is a basal level of transcript in all cell types. The... 

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