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Endo-RNase

The sole biochemical function of 2 -5A (and hence 2 -5 A synthetase) appears to be as an activator of a dormant endo-RNase, which is expressed constitutively in the cell. This RNase, known as RNase L or RNase F, cleaves all types of single-stranded RNA (ssRNA). This inhibits production of both viral and cellular proteins, thus paralyzing viral replication. Presumably, cellular destruction of the invading ssRNA will be accompanied by destruction of any additional viral components. Removal of dsRNA would facilitate deactivation of the endo-RNase, allowing translation of cellular mRNA to resume. A 2-5 phosphodiesterase represents a third enzymatic... [Pg.220]

The mode of action on poly U is similar to that on RNA. A remarkable increase of 3 terminus at an initial stage (about 25% of total residues), subsequent accumulation of UpUp or U > p, and rapid appearance of Up after a short lag time are observed. This shows that RNase T2 clearly behaves as an endonuclease for poly U as for RNA. Therefore, it should be interpreted that the apparent initial endo-... [Pg.225]

The nucleases are enzymes that hydrolyse nucleic acids, either deoxyribonucleases (DNases) that have DNA as the substrate or ribonucleases (RNases) that have ribonucleic acids as the substrate. The DNases hydrolyse the phosphodiester linkages between the deoxyribose molecules of DNA, and similarly, the RNases attack the equivalent bonds in RNA. There are many nucleases found in mammalian tissues, and as in the case of the peptidases, they can be divided into the categories endo and exo based on whether they attack bonds in the interior of the nucleic acid molecule or remove nucleosides from the end termini of the chains. They... [Pg.6]

The cyclohexene nucleoside (CeNA) derivative of adenine (55) was incorporated into ODNs using standard phosphoramidite chemistry. Incorporation of (55) into a mixed DNA sequence resulted in a slight decrease in stability opposite a DNA target, but an increase opposite RNA, similar to results found for anhydrohexitol (HNA) derivatives. However, unlike HNA, CeNA was able to activate RNase H activity. The nucleoside (55) forms duplexes with RNA that are more stable than DNAiRNA duplexes. In NMR studies, it was shown that the cyclohexenyl A nucleotide adopts a y-endo conformation in ds-DNA. A CeNA RNA duplex is cleaved by RNase H, with Km and Vmax in the same order as DNAiRNA, but the Kcat is 600-fold lower for CeNA RNA. [Pg.453]

Oligonucleotides have been prepared incorporating a number of naturally occurring sugar residues, the most common of which are arabino derivatives. Recently it was shown that hybrids of RNA and D-arabinonucleic acids (ANA) are substrates for RNase The stereochemistry at C (C -endo) is a key... [Pg.225]

Phosphorothioates interact with nucleases and DMA polymerases. These compounds are slovdy metabolized by both endo- and exonucleases and inhibit these enzymes (160, 171). The inhibition of these enzymes appears to be competitive and this may account for seme early data suggesting that phosphorothioates are almost infinitely stable to nucleases. In these studies, the oligonucleotide-to-enzyme ratio was very high and thus the enzyme was inhibited. Phosphorothioates also bind to RNase H when in an RNA-DNA duplex... [Pg.131]

In 1970, Eckstein and co-workers reported the first stereochemical study of an enzyme-catalyzed hydrolysis of a phosphate ester, the hydrolysis of the endo isomer of uridine 2, 3 -cyclic phosphorothioate (enrfo-cyclic UMPS) (72) by ribonuclease A (RNase A) 13). The hydrolysis of RNA catalyzed either by base or by RNase A proceeds by a two-step mechanism in which the 2 -hydroxyl group of a nucleotide unit within an RNA molecule acts as a nucleophile on the 3 -phosphodiester bond to displace the 5 -hydroxyl group of the neighboring nucleoside to form a 2, 3 -cyciic phosphate intermediate. RNase A then catalyzes the hydrolysis of this cyclic phosphate, mimicked by Eckstein s endo-cyclic UMPS, to yield the ultimate 3 -mononucleotide product. [Pg.97]

Retroviral RNase H (H for hybrid) which degrades the RNA strand of DNArRNA hybrids, displays both endo- and 3 -exonuclease activities. [Pg.426]

A 2 -deoxy-2 -fluoro-p-D-ribofuranoside can be considered a substitute for the natural p-D-ribose in RNA as it favors a Ci -endo sugar pucker and A-type conformation when hybridised with RNA. However, 2 -fluoro containing oligonucleotides are not substrates for RNase and are inhibitors of... [Pg.373]

RNA. A method analogous to that for DNA" has been applied to RNA, the 5 -terminally-labelled RNA being partially hydrolysed by alkali or base specific ribonucleases. The scope of this method has been extended by use of the non-specific endo-nuclease Pi and the ribonuclease from Physarium poiy cepharum which cleaves all but CpN linkages, to distinguish between oligonucleotides with Up or Cp 3 termini generated by RNase A from pancreas or RNase from Bacillus cereus. ... [Pg.201]

Figure 12. Remodeling of RNase B glycoforms through the use of endo A. Figure 12. Remodeling of RNase B glycoforms through the use of endo A.

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See also in sourсe #XX -- [ Pg.206 ]




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