Processing of Bacterial RNA

Rifampicin and other members of the rifamycin group bind to the subunit of bacterial RNA polymerase and block the formation of the first phosphodiester bond. They therefore inhibit initiation, with little effect on elongation or termination of previously initiated chains. Actinomycin D binds tightly to double-stranded DNA and prevents it from acting as a template for transcription. It binds between adjacent base pairs, particularly in G-rich regions, by a process known as intercalation. At low concentration, RNA synthesis is effectively inhibited with little effect on DNA or protein synthesis. 

Inactivates bacterial ribosomal proteins leading to a loss of vital processes of synthesizing proteins, DNA, RNA, and cell wall. Also leads to the loss of aerobic energy metabolism. It has been around since the 1950s without serious emergence of resistance because of its broad-based range of modes of action. 

Bacterial RNA polymerase, the target for the rifamycin class of antibacterial agents, is the enzyme responsible for transcription of genomic DNA in bacteria [40], Like DNA gyrase, RNA polymerase is a multifunctional, multisubunit enzyme with multiple active conformations. This increases the number of possible mechanisms of inhibition of RNA polymerase. For example, in addition to the 3 subunit, which is the apparent target for rifamycin, bacterial transcription initiation is a unique process in which the o subunit plays a unique role in the recognition of bacterial promoter sequences [41], Alternative c subunits, such... 

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... 

Where does RNA polymerase begin the process of transcription on the DNA template The DNA element on which RNA polymerase binds and initiates transcription is termed the promoter The simplest promoters are those recognized by viral RNA polymerases. Usually, these are a contiguous sequence of 15 to 30 base pairs that direct the viral RNA polymerase to the transcriptional start site (Fig. 22-2). The viral promoter sequences possess a 5 to 3 polarity, allowing you to determine which of the two DNA strands will act as the template for transcription. Bacterial promoters consist of two different but conserved DNA sequences. One of these elements is located about 10 base pairs on the 5 side of the transcriptional start site, while the other element is located about 35 base pairs to the 5 side of the transcriptional start site. Although these two elements consist of as little as six base pairs each, the... 

Figure 12.4 outlines the process of protein synthesis involving the ribosome, mRNA, a series of amino-acyl transfer RNA (tRNA) molecules (at least one for each amino acid) and accessory protein factors involved in initiation, elongation and termination. As the process is essentially the same in prokaryotic (bacterial) and eukaryotic cells (i.e. higher organisms and mammalian cells) it is surprising that there are so many selective agents which act in this area (see Fig. 12.1). 

Fig. 12.4 Outline of the process of protein synthesis (translation of messenger RNA) in bacterial cells. The four stages of synthesis are shown initiation, elongation, translocation and termination with the sites of action of antibiotics. AUG is the start codon on messenger RNA (mRNA) specifying the first amino acid in bacterial proteins, N-formylmethionine. UAG, UAA and UGA are termination codons specifying no amino acid. 30S and 50S are the subunits of the ribosome. Other protein factors involved in protein synthesis are initiation factors (IF-1,2,3), elongation factors (EF-Tu and EF-G) and release factors (RF-1,2,3).

The ribosome provides an easily accessible source of endogenous RNA-protein complexes that participate in the overall process of translation. In this section, we present protocols for obtaining salt-washed ribosomes from E. coli and mammalian cell-lines. However, if highly active vacant couples devoid of tRNAs and mRNAs is the aim, it is necessary to use more elaborate protocols that include dissociation of bacterial 70 S tight couples into subunits,17... 

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