RNase inhibition

However, there are a number of other miscellaneous biological roles played by this complex. The [Co(NH3)6]3+ ion has been shown to inhibit the hammerhead ribozyme by displacing a Mn2+ ion from the active site.576 However, [Co(NH3)6]3+ does not inhibit ribonuclease H (RNase),577 topoisomerase I,578 or hairpin ribozyme,579 which require activation by Mg2+ ions. The conclusions from these studies were that an outer sphere complex formation between the enzyme and Mgaq2+ is occuring rather than specific coordination of the divalent ion to the protein. These results are in contrast to DNase I inhibition by the same hexaammine complex. Inhibition of glucose-induced insulin secretion from pancreatic cells by [Co(NH3)6]3+ has been found.580 Intracellular injection of [Co(NH3)6]3+ into a neurone has been found to cause characteristic changes to the structure of its mitochondria, and this offers a simple technique to label neuronal profiles for examination of their ultrastructures.581... 

The LMD contains heparin that inhibits RNase H activity. The LMD buffer will also dilute the sucrose in the sample to allow overlaying on a 10 to 50% sucrosegradient. 

Heparin inhibits many enzymes, including all RNases, therefore, it is criticalfor this step. It also inhibits the labeling step therefore it needs to be removed later (by a LiCl precipitation). We did not find any comparable alternative (in efficiency and cost) to heparin. The composition and concentrations of other ingredients can be changed depending on the cell type or experiment. 

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... 

A selective method of preventing the expression of adhesion molecules or cytokines is the use of antisense oligonucleotides. These oligonucleotides are short sequences of nucleic acids complementary to mRNA sequences of specific proteins of interest. If delivered to the cytoplasmic compartment of cells these oligonucleotides are able to form a complex with their target mRNA. In this way the translation of mRNA into protein by ribosomes is inhibited. The subsequent mRNA degradation by RNAse H results in reduced expression of the protein (see also Chapter 5 for a description of antisense ohgonucleotides as therapeutic modalities). 

HIV-1, RNase H enzyme, 46 307 HIV virus, inhibition by bis(cyclam) derivatives, 45 76... 

Very few inhibitors specifically target HIV-1 RNase H activity. Illimaquinone, a natural marine product, was shown to preferentially inhibit the HIV-1 RNase H activity [113,114]. However, this compound appears to react with a sulfhydryl group in the polymerase domain and not with RNase H itself. It may be possible to use the available information on structural and biochemi-... 

Binding of RNA I to a complementary sequence in RNA II inhibits processing of primer RNA by RNAse H... 

Considerable DNase but no RNase activity results if Ca-+ is replaced by Sr-+, while Fe-+ and Cu J+ cause minimal activation (3, 40). A number of heavy metal cations inhibit DNase and RNase activities competitively with Ca-+ Hg-+, Zn2+, and Cd-+ are the most potent of these (3). Studies with synthetic substrates, to be discussed below, indicate that Ca2+ is not only required for the proper binding of substrates but also that it is required for the subsequent independent hydrolytic process. Although several divalent cations can substitute for Ca2t in the binding function, as evidenced by their competitive inhibition of enzymic activity (3) and their ability to promote nucleotide binding (62), the catalytic role of Ca2+ appears to be unique. 

The effects of inhibitors and activators on RNases Ti, N1 Ui, U2, and T2 are summarized in Table IV (5, 7, 8), showing the characteristics of each RNase. Ribonuclease Ti is strongly inhibited by 10 3M Zn2+ RNases and T2 are inhibited about half but RNases N and U2 are not inhibited. Ribonuclease T, is also strongly inhibited by 10 3M Ag+, while all other RNases are inhibited about half. But 10 3 M Cu2+ strongly inhibits RNase T2 and only about half inhibits the other RNases. All five RNases are not inhibited by 10 2 M ethylenediaminetetraacetate (EDTA) and 10-3 M ICH2COOH. No metallic cofactor is required for their action. 

Heparin, which inhibits RNase A, does not inhibit RNase Ti, nor does a natural RNase A inhibitor from rat liver (20), or Aspergillus orysae nuclease inhibitor (21). 

The same enzyme has been highly purified from another strain (strain K) of Bacillus subtilis, and their properties have been fully investigated by Yamasaki and Arima (119, 120). They have confirmed the findings by Nishimura and Maruo and have found, moreover, that ATP and dATP strongly inhibit the enzyme. Yamasaki and Arima suggested that ATP might participate in the regulation of intracellular RNase activity. 

RNase M Np, Non-s Zn2+, Cu2+ other effectors kinetic data photooxidation inhibition by nucleotides 166)... 

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