MRNA synthesis

Biosynthesis. CRE is derived from a precursor of 196 amino acids (84,85). This gene contains one copy of CRE, which is flanked by double basic amino acids. The amino acid sequence of the CRE precursor suggests that it may arise from proteins related to POMC and neurophysins (31). The CRE precursor contains a cAMP responsive element which aHows stimulation of mRNA synthesis when intraceHular levels of cAMP are increased (86). 

Pig. 3. Representation of promoter sites on the pro-enkephalin gene. The numbers represent the distance in nucleotides from the pro-enkephalin initiation codon the arrow indicates the direction of transcription. The TATA promoter box occurs immediately before the pro-enkephalin initiation site the AP-2 site, which binds immediate-early gene products, is 70 nucleotides upstream, and the CRE site, which binds a regulatory protein involved in cAMP induction of mRNA synthesis, is 107 nucleotides upstream from the initiation codon. The expanded section shows that the CRE site actually consists of two elements, ENKCRE-1 and ENKCRE-2, which separately confer cAMP sensitivity to pro-enkephalin mRNA synthesis. 

Regulation of mRNA synthesis Regulation of gene expression... 

Chang, C.C., Konno, S., Wu, J.M. (1991). Enhanced expression of heat shock protein and mRNA synthesis by type I interferon in human HL-60 leukemic cells. Biochem Inti. 24, 369-377. 

Eukaryotic mRNA synthesis results in a pre-mRNA precursor that contains extensive amounts of excess RNA (introns) that must be precisely removed by RNA splicing to generate functional, translatable mRNA composed of exonic coding and noncoding sequences. 

Virus messenger RNA In order for the new virus-specific proteins to be made from the virus genome, it is necessary for new virus-specific RNA molecules to be made. Exactly how the virus brings about new mRNA synthesis depends upon the type of virus, and especially upon whether its genetic material is RNA or DNA, and whether it is single-stranded or double-stranded. Which copy is read into mRNA depends upon the location of the appropriate promoter, since the promoter points the direction that the RNA polymerase will follow. In cells (uninfected with virus) all mRNA is made on the DNA template, but with RNA viruses the situation is obviously different. 

A virus-specific RNA RNA polymerase is needed, since the cell RNA polymerase will generally not copy double-stranded RNA (and ribosomes are not able to translate double-stranded RNA either). A wide variety of modes of viral mRNA synthesis are outlined in Figure. By convention, the chemical sense of the mRNA is considered to be of the plus (+) configuration. The sense of the viral genome nucleic acid is then indicated by a plus if it is the same as the mRNA and a minus if it is of oppposite sense. If the virus has double-stranded DNA (ds DNA), then mRNA synthesis can proceed directly as in uninfected cells. However, if the virus has a singlestranded DNA (ss DNA), then it is first converted to ds DNA and the latter serves as the template for mRNA synthesis with the cell RNA polymerase. 

If the virus has double-stranded RNA (ds RNA), this RNA serves as a template in a manner analogous to DNA. There are three classes of viruses with ss RNA and they differ in the mechanism by which mRNA is synthesized. In the simplest case, the incoming viral RNA is the plus sense and hence serves directly as mRNA, and copies of this viral RNA are also copied to make further mRNA molecules. In another class, the viral RNA has a minus (-) sense. In such viruses a copy is made (plus sense) and this copy becomes the mRNA. In the case of the retroviruses (causal agents of certain kinds of cancers and AIDS), a new phenomenon called reverse transcription is seen, in which virion ss RNA is copied to a double-stranded DNA (through a ss DNA intermediate) and the ds DNA then serves as the template for mRNA synthesis (thus ss RNA ss DNA ds DNA). Retrovirus replication is of unusual interest and complexity. 

Iron homeostasis in mammalian cells is regulated by balancing iron uptake with intracellular storage and utilization. As we will see, this is largely achieved at the level of protein synthesis (translation of mRNA into protein) rather than at the level of transcription (mRNA synthesis), as was the case in microorganisms. This is certainly not unrelated to the fact that not only do microbial cells have a much shorter division time than mammalian cells, but that one consequence of this is that the half-life of microbial mRNAs is very much shorter (typically minutes rather than the hours or often days that we find with mammals). This makes it much easier to control levels of protein expression by changing the rate of specific mRNA synthesis by the use of inducers and repressors. So how do mammalian cells... 

It has been reported that ceruloplasmin increases iron uptake into cultured human cells (Mukhopadhyay et al, 1998), although this apparently contradictory in vitro observation must be set against the in vivo evidence presented above from both animal and human studies. Plasma ceruloplasmin levels increase markedly in anaemia, consistent with a physiological role in tissue iron mobilization, and this effect is due to transcriptional activation of ceruloplasmin mRNA synthesis (Mukhopadhyay et al, 2000). 

Meso-tetraaryl porphyrins, 14 552 Mesothelioma, 3 316 Messenger ribonucleic acid (mRNA), expression profiling and, 13 354 Messenger RNAs (mRNA), 12 449, 454, 473, 515 17 614, 627 20 824. See also mRNA synthesis... 

Important pathways requiring SAM include synthesis of epinephrine and of the 7-methylgua-nine cap on eukaryotic mRNA, Synthesis of SAM from methionine is shown in Figure T17-3. After donating the methyl group, SAM is converted to homocysteine and remethylated in a reaction catalyzed by N-methyl THF-homocysteine methyltransferase requirii both vitamin Bj2 and N-meth d-THF. The methionine produced is once again used to make SAM. 

Perhaps a bit more subtle than those agents that react chemically with DNA are those that insert themselves between the stacked bases of the DNA double helix— intercalation. This alters the regular structure of the DNA molecule and may lead, for instance, to inhibition of mRNA synthesis. The structures of the intercalcating agents are generally quite complex and I will spare you the complexity. However, three names may be familiar—dactinomycin (Actinomycin D), daunorubicin (daunomycin), and doxorubicin (Adriamycin)— and intercalation is how they work. All three are natural products and were isolated from the fermentation broths of Streptomyces species. 

Figure 12.17 Sites at which insulin stimulates protein synthesis in a muscle. The sites are indicated by 0. Insulin has its anabolic effect on protein synthesis in muscle by affecb ng six processes or reactions (i) it inhibits protein degradab on in the muscle (ii) it sb mulates amino acid transport from the blood into the muscle (iii) it stimulates the inib ab on-reacb on of the pathway for protein synthesis, i.e. formab on of the complex (tRNA-amino acid-mRNA-ribosomal RNA) (iv) it increases the rate of mRNA synthesis, and therefore the number of mRNA molecules (v) it stimulates ribosomal RNA synthesis (vi) it sb mulates elongabon of the pepbde (see Chapter 20).

Iwata T, Watanabe T, Kufe DW. Effects of 5-fluorouracil on globin mRNA synthesis in murine eryth-roleukemia cells. Biochemistry 1986 25 2703-2707. 

Muller Igaz L, Vianna MR, Medina JH, Izquierdo I (2002) Two time periods of hippocampal mRNA synthesis are required for memory consolidation of fear-motivated learning. J Neurosci 22 6781-6789... 

A number of papers on the biological activity of gibberellins and their derivatives have appeared. The stimulation of plant mRNA synthesis by gibberellic acid has been noted. 

Dissolve the pellet in sterilized distilled water and quantitate the DNA concentration by spectrophotometer, then use as the template for mRNA synthesis (tee Note 12). 

Eischer, A., Franco, A., and Oberholzer, T. (2002). Giant vesicles as microreactors for enzymatic mRNA synthesis. Chem. Bio. Chem., 3 (5), 409-17. 

Quinolones (bacteriostatic inhibit DNA gyrase) e.g., ciprofloxacin, cinoxacin, enoxacin, norfloxacin Rifampin (bactericidal blocks mRNA synthesis in bacteria, inhibits RNA polymerase)... 

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