Transcription factors transcriptional process

Degradation of RNA DNA-dependent RNA polymerase Transcription factors RNA processing Other Translation... 

Transcription Factors Endogenous substances, usually proteins, which are effective in the initiation, stimulation, or termination of the genetic transcription process. [NIH]... 

Once integrated into the host chromosome, the assembly of new viral particles necessitates the prodnction of viral RNA transcripts and proteins. Initiation of viral transcription is also an RNA independent process where host transcription promoters and enhancer elements such as NF-kB bind to the 5 -LTR. The host transcriptional complex is then recrnited and transcription commences.Once transcription has been initiated, RNA and RNA-RNA interactions play a critical role in mediating the production of viral transcripts. The multiprotein transcription complex has a recognition factor for nonhost DNA and quickly releases from viral DNA, creating short, abortive transcripts. Processing and nuclear export of these transcripts leads to the translation of the HIV Tat protein, a small early-phase viral protein (Figure 10.4) that plays a key role in the ultimate formation of fnll-length viral RNA transcripts. 

Further examples of substrates of protein kinase C are the epidermal growth factor receptor (see Chapter 8), a Na7H exchanger protein, and Raf kinase (Chapter 9). Activation of protein kinase C may, as the examples show, act on other central signal transduction pathways of the cell it may have a regulating activity on transcription processes and it is involved in the regulation of transport processes. Many substrates of protein kinase C are membrane proteins and it is evident that membrane association of protein kinase C is of great importance for the phosphorylation of these proteins. 

The Jak-Stat signal transduction is an example of a signaling pathway in which a signal is coupled, in the form of a tyrosine phosphorylation, directly to activation of a transcription factor. In contrast to other signaling pathways that also regulate transcription processes, e. g., the Ras/MAPK pathway, the Jak-Stat pathway is impressive in its simple concept and the small number of components involved. 

We have seen that prokaryotes have a single RNA polymerase that is responsible for the synthesis of all three kinds of prokaryotic RNA— mRNA, tRNA, and rRNA. The polymerase can switch a factors to interact with different promoters, but the core polymerase stays the same. The transcription process is predictably more complex in eukaryotes than in prokaryotes. Three RNA polymerases with different activities are known to exist. Each one transcribes a different set of genes and recognizes a different set of promoters ... 

As mentioned in Section 7.2.1, at the 5 end of mRNA molecules to be translated by eukaryotic cells, there is the characteristic Cap structure. It consists of a 7-methylated guanine residue linked through three phosphates to the first residue of the mRNA. A noncapped mRNA is not translated in eukaryotic cells. Not only is this structure essential for recognition of the mRNA by the translation machinery (the cap is recognized by the initiation factor 4 eIF4), but it also protects the 5 end of the mRNA against exonucleases. Similarly to what was described for the poly-A tail, either the Cap structure is incorporated during the transcription process or it is added afterward on the in vitro transcribed mRNA. 

Much less is known about termination of transcription in eukaryotes than in bacteria. Once transcribed, specific termination sequences of mRNA are bound by protein complexes (such as CPSF cleavage and poly(A)denylation specificity factor, and CstF cleavage stimulation factor) that process cleavage of the message and subsequent poly(A)denylation. RNA polymerase continues transcription for up to several hundred nucleotides before dissociating from the DNA. 

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