Ribosome inhibitors targeted

I. Aminoglycoside-modifying Enzyme Inhibitors Targeting Ribosomal RNA... 

Rapamycin is an immunosuppressive diug and an inhibitor of S6K1 (also known as p70S6-kinase) which phosphorylates ribosomal S6 protein. S6K1 is activated in response to insulin via activation of Akt. Rapamycin binds to a specific target protein (mTOR, mammalian target of rapamycin) which is functionally located downstream of Akt, but upstream... 

In eukaryotes, translation initiation is rate-limiting with much regulation exerted at the ribosome recruitment and ternary complex (elF2 GTP Met-tRNAjMet) formation steps. Although small molecule inhibitors have been extremely useful for chemically dissecting translation, there is a dearth of compounds available to study the initiation phase in vitro and in vivo. In this chapter, we describe reverse and forward chemical genetic screens developed to identify new inhibitors of translation. The ability to manipulate cell extracts biochemically, and to compare the activity of small molecules on translation of mRNA templates that differ in their factor requirements for ribosome recruitment, facilitates identification of the relevant target. 

The discovery and characterization of novel small molecule inhibitors that target the ribosome recruitment step of translation initiation is extremely important in order to validate translation initiation as a chemotherapeutic target. Rapamycin, an inhibitor of TOR (target of rapamycin) complex I... 

Transcriptional inhibitors could be used simultaneously. Rifampicin blocks chloroplast and mitocondrian RNA synthesis [23, 24], while tagetitoxin is a very specific inhibitor of chloroplast RNA polymerase [25]. Treatment with these antibiotics does not inhibit Rubisco SSU synthesis since the promoter is part of the nuclear genome, while the cytosolic ribosomes are not affected by streptomycin. Therefore SSU promoters can be used to drive transgene expression and facilitate the accumulation of recombinant proteins. Expressed proteins are targeted to a suitable cellular compartment, such as the cytoplasm, apoplastic space or chloroplast, depending on the nature of the protein. 

What are the mechanisms by which trichothecenes exert their transcriptional and post-transcriptional effects The 60S ribosomal subunit is a well-known molecular target of trichothecenes in leukocytes and other actively proliferating eukaryotic cells,3 whereas attempts to demonstrate alternative receptors have not been successful.37 38 Translational inhibitors that bind to ribosomes rapidly activate mitogen-activated protein kinases (MAPKs) and apoptosis via a mechanism termed the ribotoxic stress response. 39-40... 

Even for antimicrobial drugs wich have the same mode of action, the mechanisms of actions in molecular terms can be quite different. An instructive example of this is the body of knowledge on actions of inhibitors of protein synthesis at the ribosomal level66). Since the mechanistic details of protein biosynthesis as well as of DNA replication are still incompletely resolved, studies on mechanisms of action of inhibitors of these biosynthetic processes frequently remain inconclusive when the target reaction is not known. Each problem of the mechanism of action of a chemotherapeutic drug becomes an individual research problem in its own right, after the mode of action has been elucidated in the manner described in this article. 

In both bacteria and eucarya the susceptibility to certain ribosome-targeted inhibitors correlates with specific primary structural features of rR24A, or with features of the ribosomal domain that acts as the antibiotic binding sites. Firstly, resistance to specific ribosome-directed drugs is conferred by single-base changes within phylogenetically... 

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