Protein-coding genes transcription factors

DNA-binding proteins. A whole series of oncogenes code for transcription factors. Particularly important for cell proliferation are myc, as well as fos and jun. The protein products of the latter two genes form the transcription factor AP-1 as a heterodimer (see p. 244). 

Those protein-coding genes that have an initiator element instead of a TATA box (see above) appear to need another protein(s) that binds to the initiator element and facilitates the binding of TBP. The other transcription factors then bind to form the transcription initiation complex in a similar manner to that described above for genes possessing a TATA box promoter. 

Fig. 1. Control regions that regulate transcription of a typical eukaryotic protein-coding gene. Although shown as distinct entities here for clarity, in vivo the different regulatory proteins bound to the control elements and distant enhancers interact with each other and with the general transcription factors of the transcription initiation complex to modulate the rate of transcriptional initiation.

Typically each protein-coding gene in a eukaryotic cell has several control elements in its promoter (Fig. 1) and hence is under the control of several transcription factors which interact with each other and with the transcription initiation complex by protein protein interaction to determine the rate of transcription of that gene. 

Secretion of ecdysone starts the many biochemical processes that are necessary for the molting. The cells in the epidermis are stimulated to produce a new cuticle, and when ready, the insect will creep out of its old skin. The molecular mechanism of ecdysone has been studied in some detail. The molecular target of ecdysone and other ecdysteroids consists of at least two proteins, the ecdysteroid receptor (EcR) and ultraspiracle (USP). Both EcR and USP are members of the steroid hormone receptor superfamily with characteristic ligand-binding domains. An EcR-USP-ecdysteroid complex is formed, which activates several genes that code for transcription factors, i.e., proteins that activate or repress the activity of other genes, and the appropriate amounts of proteases and other enzymes necessary to degrade old structures and rebuild new ones are formed in a time-controlled sequence. 

HIV-1 gene coding for the Envelope surface and transmembrane proteins ETS-1 transcription factor feline immunodeficiency vims HIV-1 gene coding for the capsid and matrix stmctural proteins... 

The various transcription-control elements found in eukaryotic DNA are binding sites for regulatory proteins. In this section, we discuss the identification, purification, and structures of these transcription factors, which function to activate or repress expression of eukaryotic protein-coding genes. 

Initiation complex - All of the protein-coding genes in eukaryotes are transcribed by RNA polymerase II (pol II) This enzyme also transcribes some of the small nuclear RNAs involved in splicing (see here). Like other RNA polymerases, pol II is a complex, multisubunit enzyme, but not even its numerous subunits are sufficient to allow pol II to initiate transcription on a eukaryotic promoter. To form a minimal complex capable of initiation, at least five additional protein factors are needed Figure 28.24 and listed in Table 28.4. The minimal unit involves the TATA binding protein, (TBP), but in vivo formation of the complex probably always uses TFllD, a multi-subunit structure incorporating both TBP and TATA binding associated factors (TAFs). 

The TATA box-binding protein (TBP) is a basic transcription factor absolutely required for transcription by the three nuclear RNA polymerases (7). RNA polymerase II transcription of many protein coding genes requires direct contact of the DNA by TBP, at a sequence called the TATA box, which is located approximately 30 basepairs upstream of the transcription initiation site (2). This complex directs the assembly of the remaining basic transcription factors into a preinitiation complex (i). 

Homeoboxes code for homeodomains, sequences of 60 amino acids that function as the DNA-binding regions of transcription factors. Each homeo-box gene in Drosophila is expressed only in its own characteristic subset of embryonic cells, and almost every embryonic cell contains a unique combination of homeodomain proteins. 

One such hypotheses submits that most antidepressants enhance the expression of cyclo-AMP response element binding protein (CREB), which is a transcription factor that after phosphorylation binds to cyclo-AMP response elements localized in the promoter region of many genes including that coding for brain... 

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