Transcription RNA polymerases

The Xenopus transcription factor IIIA not only acts as an essential RNA polymerase transcription factor for the expression of the 5S rRNA gene, it also binds to the 5S rRNA to form a 7S ribonucleoprotein particle that stabilizes the RNA until it is required for ribosome assembly and facilitates nuclear export of the 5S rRNA. Indeed, it was originally shown to be the protein component associated with 5S rRNA in the 7S particle in Xenopus oocytes before it was recognized as a transcription factor. How, we may ask, can this protein not only recognize specific DNA sequences in the 5S rRNA gene upstream region, but also recognize different, but equally specific, sequences in 5S rRNA ... 

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

To influence the activity of RNA polymerase, transcription factors bind to DNA at enhancer sites and/or promoter sites. Four different structures of these factors are known. They possess structures that allow specific binding to DNA. They are given names that indicate the key protein domains that encourage this binding, as follows ... 

As in procaryotes, the elementary steps of initiation, elongation and termination can be distinguished in eucaryotic transcription. Aside from the specific RNA polymerases, transcription in eucaryotes requires the action of numerous other proteins which are collectively known as transcription factors. Transcription factors are required at the level of initiation, elongation, and termination and are accordingly known as initiation factors, elongation factors and termination factors of transcription. 

Wehrli, W., Staehelin, M. Interaction of rifamycin with RNA polymerase. In Proc. 1st Int. Lepetit Colloq. RNA Polymerase. Transcript. Amsterdam-London North-Holland Publ. Co. 1970, p. 65... 

T7 RNA polymerase transcription past (—)-Irans-anli- N2- D B a,l] P D E -dG results in partial blockage with about 25% bypass (Figure 17.5). While full-length transcripts exhibit no base misincorporations, the majority of truncated transcripts either end opposite the lesion with an incorrect base, usually an adenine, or one base before the lesion. In contrast, (—)-trans-anti-N2-DB[a,l]PDE-dG posed a strong block to human RNA Pol II, permitting little read-through at about 4% (Figure 17.5). In the case of N2-DB a,I PDE-dG, the majority of the shortened transcripts... 

Roth, R.B., Amin, S., Geacintov, N.E., and Scicchitano, D.A. (2001) Bacteriophage T7 RNA polymerase transcription elongation is inhibited by site-specific, stereospecific benzojc] phenanthrene diol epoxide DNA lesions. Biochemistry, 40, 5200-5207. 

In eukaryotes, the mechanisms for terminating transcription differ for each of the three RNA polymerases. Transcription of pre-rRNA genes by RNA polymerase I is terminated by a mechanism that requires a polymerase-specific termination factor. This DNA-binding protein binds to a specific DNA sequence downstream of the transcription unit. Efficient termination requires that the termination factor bind to the template DNA in the correct orientation. Purified RNA polymerase III terminates after polymerizing a series of U residues. The deoxy(A) -ribo(U) DNA-RNA hybrid that results when a stretch of U s are synthesized is particularly unstable compared with all other base-paired sequences. The ease with which this hybrid can be melted probably contributes to the mechanism of termination by RNA polymerase III. 

Different mechanisms of transcription termination are employed by each of the eukaryotic nuclear RNA polymerases. Transcription of most protein-coding genes is not... 

See also Initiation and Elongation, Structure of RNA Polymerase, Transcription Regulation in Phage, Lactose Operon Regulation, Supercoiling (from Chapter 4)... 

In the absence of lactose (Figure 17.9b), the regulator gene produces an mRNA molecule which gives rise to a protein which has an affinity for the operator site. Since the promoter and operator sites overlap, the operator-bound protein prevents the attachment of RNA polymerase. Transcription of the structural genes denoted as lacZ, lac Y and lacA is inhibited, i.e. repressed, therefore the protein product of the regulator gene is termed a... 

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