Enzymes viruses, unique

The starting material for sequence analysis is usually a defined duplex DNA fragment purified from a restriction enzyme digest or obtained by a cleavage, at a unique site, of a defined circular DNA from a plasmid, phage or virus. Unique ends may also originate in... 

Enzymes in viruses We have stated that virus particles do not carry out metabolic processes. Outside of a host cell, a virus particle is metabolically inert. However, some viruses do contain enzymes which play roles in the infectious process. For instance, many viruses contain their own nucleic acid polymerases which transcribe the viral nucleic acid into messenger RNA once the infection process has begun. The retroviruses are RNA viruses which replicate inside the cell as DNA intermediates. These viruses possess an enzyme, an RNA-dependent DNA popo called reverse transcriptase, which transcribes the information in the incoming RNA into a DNA intermediate. It should be noted that reverse transcriptase is unique to the retroviruses and is not found in any other viruses or in cells. 

GPRT- defective cells appear in population. Using the method of the selective pressure by 5-BDU and 8-Ag, the mutant cultures of cells, defective by the indicated enzymes, are obtained. The intraspecific and interspecific hybrid cultures of cells are firstly obtained in the laboratory of the cellular biotechnology, A4H (SPEV TK- x lymphocytes of horse) and others. Hybrid cultures possess the unique properties. They are the ability to grow in the monolayer and in suspension, the high sensitiveness to the viruses. Hybrid cultures PO-TK-KHLO, PO-TK-KHSO are sensible to the agent scrappy, what allows using them for the study of diseases, caused by prions. 

Coding versus Template Strands The RNA genome of phage Q/3 is the nontemplate or coding strand, and when introduced into the cell it functions as an mRNA. Suppose the RNA replicase of phage Q/3 synthesized primarily template-strand RNA and uniquely incorporated this, rather than nontemplate strands, into the viral particles. What would be the fate of the template strands when they entered a new cell What enzyme would such a template-strand virus need to include in the viral particles for successful invasion of a host cell ... 

Persistent viral infection is a difficult challenge for antiviral chemotherapy. Retroviruses as a class are often found to be responsible for persistent viral infections. Retroviruses are unique RNA viruses characterized by the transcription of their single-stranded RNA into the double-stranded DNA of the host cell using the viral enzyme reverse transcriptase. AIDS is an example of such a persistent and latent human viral infection. 

Enzymes that catalyze the synthesis of DNA using an RNA template are known as reverse transcriptases. The first reverse transcriptase discovered was encoded by an RNA retrovirus. This enzyme is needed in the virus replication cycle. Some animal viruses pass through an RNA intermediate and also require a reverse transcriptase to replicate the viral DNA. Similarly, a number of transposable elements found in cellular chromosomes replicate through RNA intermediates they usually encode a reverse transcriptase. A unique reverse transcriptase called telomerase is used to synthesize the DNA at the ends of linear eukaryotic chromosomes. 

The enzyme controlled by the E. coli genes recB and recC has several activities in vivo associated with substrate DNA, notably the degradation of single- and double-stranded DNA. Activity depends upon the presence of K+, which is suggested to maintain the conformation of the enzyme in the active form.98 Many DNA polymerases are stimulated as much as five-fold by cations, particularly K+ and NH4+, at concentrations up to 50 mM.99 At higher concentrations of M+, most DNA polymerases are inhibited. Inhibition by monovalent cations has been used to distinguish between DNA polymerase-a and -j8 from eukaryotic cells, since the latter enzyme is not inhibited by concentrations as high as 300 mM. A DNA polymerase coded for by herpes virus is uniquely stimulated by both Na+ and K+. Little is known about the mechanism of action of the IA cations in these cases. 

Although a large number of candidates were synthesized, none of the resulting compounds demonstrated significantly increased activity against influenza virus sialidase. Moreover, the interactions of individual substituents on the benzene ring with the active site were not found to be additive. The overall interaction of the molecules with the active site of the enzyme was dependent upon the electronic and steric interaction of each unique substituent, which made the design of inhibitors difficult.111 No compound of this family has proceeded to clinical trials. 

These drugs also inhibit our own enzymes and are very toxic, Biologists then discovered an alternative point of attack. An enzyme unique to the virus cuts up long proteins into small pieces essential for the formation of new HIV particles. If this enzyme could be inhibited, no new viruses would be formed, and the inhibitor should not damage human chemistry. Several companies invented HIV protease inhibitors, which looked more like small pieces of proteins with the weak link of the amide bond replaced by a more stable C-C bond. 

Viruses vary greatly. Simple viruses make parsimonious use of a few gene products, gaining additional functionality from host proteins. Others are complicated machines that encode many of the structural and enzymatic proteins needed for their own replication. This review, first, focuses on proteins whose structure or function is primarily associated with viruses. It does not cover the myriad of enzymes encoded by larger viruses that are homologous to cellular proteins. Second, it is restricted to those proteins whose structures are known at near atomic resolution. This will include the building blocks of symmetrical virus capsids and cores, and key membrane proteins of some enveloped viruses, and a few enzymes with function unique to viruses. 

A unique biochemical target in the HIV-1 replication cycle was revealed when HIV protease was cloned and expressed " in Escherichia coli. HIV protease is an enzyme that cleaves gag-pro propeptides to yield active enzymes that function in the maturation and propagation of new virus. The catalytically active protca.se is a. symmetric dimer of two identical 99 amino acid subunits, each contributing the triad Asp-Thr-Gly to the active site." The homodimer is unlike monomeric asparlyl protea.ses (renin, pepsin, cathep-sin D). which also have different. substrate specificities. The designs of. some inhibitors for HIV-1 protease exploit the C2 symmetry of the enzyme. HIV-1 protease has active site speclnc ity for the triad Tyr-Phe-Pro in the unit Ser-(Thr)-Xaa-Xaa-Tyr-Phc-Pm. whenr Xaa is an arbitrary amino acid. 

A unique HAS enzyme occurs in the virus that infects an algae Pasteurella multocida (pmHAS) that is quite different from all other HA synthases [94]. This is in a class by itself and will not be considered further. 

In other studies, three strains of Epstein-Barr virus and herpes simplex types 1 and each gave unique restriction enzyme patterns. 

After internalization, the virus is uncoated in preparation for replication. The genetic material of HIV is positive-sense singlestrand RNA (ssRNA) the virus must transcribe this RNA into DNA to optimally replicate in human cells (transcription normally occurs from DNA to RNA—HIV works backward, hence the name retrovirus). To do so, HIV is equipped with a unique enzyme, RNA-dependent DNA polymerase (reverse transcriptase). Reverse transcriptase first synthesizes a complementary strand of DNA using the viral RNA as a template. The RNA portion of this DNA-RNA hybrid is then partially removed by ribonuclease H (RNase H), allowing reverse transcriptase to complete the synthesis of a double-stranded DNA (dsDNA) molecule. Unfortunately, the fidelity of reverse transcriptase is poor. 

In the case of viruses, the window for selective enzyme inhibition is particularly narrow. Viruses are not complete organisms in that they use the host s own enzymes for much of their required metabolism. Thus, selective targeting of viruses usually involves a very small number of enzymes that are unique to the virus itself. This is one of the reasons why viruses are very difficult to treat. In short, the opportunities to inhibit specific virus enzymes are very few. Some of the agents that are used for some news-worthy viruses include acylovir and dideoxyinosine (Figure 9). These are used to treat Herpes and HIV viruses, respectively. Apparently, certain viral enzymes will bind to these structures while the host s own enzymes will not. Attempts to target other viral enzymes is a current intense area of research. 

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