Nuclei, enzymes isolation

No. Eukaryotic RNA polymerases have been isolated from many tissues, and in all cases, three distinct enzymes have been found in the nucleus. All contain a number of polypeptide subunits and are complex in structure, RNA polymerase I is known to be involved specifically in the transcription of rRNA genes. RNA polymerase II gives rise to transcripts that are subsequently processed to yield mRNA. RNA polymerase 111 is responsible for the transcription of the tRNA genes and a small ribosomal RNA gene that yields a species called 55 RNA. The three polymerases are distinguishable from one another by their differential sensitivity to the drug a-amanitin (the toxic principle of the mushroom Amanita phalloides), which does not affect bacterial RNA polymerase. RNA polymerase... 

After deglucosylation, the pathway proceeds through a 4,21-Dehydrogeissoschizine derivative to ajmalicine (an a-Blocking spasmolytic agent, used for tinnitus and cranial trauma with an ergot derivative). If cyclization occurs between C-17 and C-18, the yohimbine nucleus is produced, whose derivatives include the Rauvolfia alkaloids reserpine and resdnnamine (antihypertensive activity). Ajmaline, formerly used as an antiarrythmic, also occurs in Rauvolfia species, and several of the enzymes in the pathway have been isolated. Recent considerations suggest that the C-16-C-5 bond may be formed before the N-4-C-21 bond (Fig. 38). 

The use of biological methods has a small, but significant niche in synthetic heterocyclic chemistry, being used both on a research scale and for fine-chemicals production. The processes may use isolated enzymes or whole microorganisms, the main reactions being oxidations of a heterocyclic nucleus or of side-chains, but other reaction types are also used, for example enzymatic catalysis has been used to ribosylate purines and related bases by reaction with a 7-aUcylated nucleoside.""... 

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