MRNA polymerase

Amanita phalloides Mycotoxins, especially a-amatoxin, are extremely hepatotoxic as a result of the inhibition of mRNA polymerase B and the blocking of RNA synthesis. The lethal dose is approx. 0.1 mg amatoxin/kg BW (1-3 fungi = 10-50 g), depending on the patient s age and state of health as well as the respective degree of intestinal absorption and diffusion in the tissue. The heat-resistant mycotoxins (amanitines) are capable of enterohepatic recirculation, (s. pp 383, 571)... 

C. RNA polymerase I produces the large rRNA precursor. Polymerase II produces hnRNA (and consequently mRNA). Polymerase III produces tRNA and 5S rRNA. 

RNA molecules destined to become mRNA. Polymerase III synthesizes 5S rRNA and the tRNAs. 

Figure 9.5. (a) Transcription of the gene by mRNA polymerase starts at the operator site in promoter, (b) Lac repressor binds the operator site and prevents the transcription, (c) In the presence of an inducer like IPTG, the inducer binds the repressor and prevents it from binding to the operator. The operator site is now free and mRNA polymerase can start the transcription. 

Add RNase H, DNA polymerase, and dATP, dTTP, dGTP, dCTP mRNA degraded by RNase T... 

The conversion of the information in DNA into proteins begins in the nucleus of cells with the synthesis of mRNA by transcription of DNA. In bacteria, the process begins when RNA polymerase recognizes and binds to a promoter... 

Due to the large amount of DNA present within the nucleus it must be carefully packaged. In the resting cell DNA is tightly compacted around basic histone proteins, excluding the binding of the enzyme RNA polymerase II, which activates the formation of mRNA. This conformation of the chromatin structure... 

Quantitative polymerase chain reaction, also called real-time RT-PCR or QPCR, is a method which employs insertion of a signal, such as fluorescence or enzyme activity, into PCR products generated by RT-PCR to determine the amount of messenger RNA (mRNA) in a tissue accurately. 

Although we will stick to the IL-6 gene, it should be mentioned at the side that two other RNA polymerases exist in mammalian cells responsible for the synthesis of RNA molecules, which are not translated into proteins ribosomal (rRNA), transfer (tRNA), small nuclear (snRNA), small nucleolar (snoRNA), and some of the recently discovered microRNAs and piRNAs. These RNA molecules act in the process of translation and mRNA turnover. Micro and piRNAs are probably extremely important in the definition of stem cells and of differentiation programs. Some of them are synthesized by RNA polymerase II. 

The moderately repetitive sequences, which are defined as being present in numbers of less than 10 copies per haploid genome, are not clustered but are interspersed with unique sequences. In many cases, these long interspersed repeats are transcribed by RNA polymerase II and contain caps indistinguishable from those on mRNA. 

The primary transcripts generated by RNA polymerase II—one of three distinct nuclear DNA-depen-dent RNA polymerases in eukaryotes—are promptly capped by 7-methylguanosine triphosphate caps (Figure 35-10) that persist and eventually appear on the 5 end of mature cytoplasmic mRNA. These caps are necessary for the subsequent processing of the primary transcript to mRNA, for the translation of the mRNA, and for protection of the mRNA against exonucleolytic attack. 

Poly(A) tails are added to the S end of mRNA molecules in a posttranscriptional processing step. The mRNA is first cleaved about 20 nucleotides downstream from an AAUAA recognition sequence. Another enzyme, poly(A) polymerase, adds a poly(A) tail which is subsequently extended to as many as 200 A residues. The poly(A) tail appears to protect the S end of mRNA from S —> S exonuclease attack. The presence or absence of the poly(A) tail does not determine whether a precursor molecule in the nucleus appears in the cytoplasm, because all poly(A)-tailed hnRNA molecules do not contribute to cytoplasmic mRNA, nor do all cytoplasmic mRNA molecules contain poly(A) tails... 

There are three distinct nuclear DNA-dependent RNA polymerases in mammals RNA polymerases I, II, and III. These enzymes control the transcriptional function—the transcription of rRNA, mRNA, and small RNA (tRNA/5S rRNA, snRNA) genes, respectively. 

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