Reverse transcriptase requirements

Reverse transcriptase requires 10 to 15 bases complementary to target messenger... 

These drugs usually act by inhibiting the polymerases or reverse transcriptases required for nucleic acid synthesis. They are usually analogues of the purine and pyrimidine bases found in the nucleic acids (Figure 7.16). Their general mode of action often involves conversion to the corresponding triphosphate by the host... 

Reverse transcriptase requires the following for the conversion of a single-strand RNA into a double-strand DNA. 

The viruses responsible for AIDS are human immunodeficiency virus 1 and 2 (HIV 1 and HIV 2) Both are retroviruses, meaning that their genetic material is RNA rather than DNA HI Vs require a host cell to reproduce and the hosts m humans are the T4 lymphocytes which are the cells primarily responsible for inducing the immune system to respond when provoked The HIV penetrates the cell wall of a T4 lymphocyte and deposits both its RNA and an enzyme called reverse transcriptase inside There the reverse transcriptase catalyzes the formation of a DNA strand that is complementary to the viral RNA The transcribed DNA then serves as the template from which the host lymphocyte produces copies of the virus which then leave the host to infect other T4 cells In the course of HIV reproduction the ability of the T4 lymphocyte to reproduce Itself IS compromised As the number of T4 cells decrease so does the body s ability to combat infections... 

Reverse transcriptase inhibitors are also used against certain viruses which although they are not retroviruses do require re verse transcriptase to repro duce The virus that causes heptatitis B is an example... 

Rifampicin has also shown antiviral activity but at levels 500—1000 times greater than required for antibacterial activity (130,140—142). Rifampicin shows promise in the treatment of leprosy (130,143). A large number of rifampicinlike derivatives are potent inhibitors of reverse transcriptase (123,144-148). 

Nucleoside reverse transcriptase inhibitor (NRTI)/nucleotide reverse transcriptase inhibitor (NtRI) A modified version of a naturally-occurring nucleoside or nucleotide that prevents human immunodeficiency virus (HIV) replication by interfering with the function of the viral reverse transcriptase enzyme. The nucleoside/nucleotide analog causes early termination of the proviral DNA chain. For activity, an NRTI requires three phosphorylation steps once inside the cell, whereas an NtRI has a phosphate group attached and needs only two phosphorylation steps inside the cell for activity. 

The nonnucleoside reverse transcriptase inhibitors (NNRTIs), used in the treatment of AIDS, provide interesting examples of clinically relevant noncompetitive inhibitors. The causative agent of AIDS, HIV, belongs to a virus family that relies on an RNA-based genetic system. Replication of the vims requires reverse transcription of the viral genomic RNA into DNA, which is then incorporated into the genome of the infected host cell. Reverse transcription is catalyzed by a virally encoded nucleic acid polymerase, known as reverse transcriptase (RT). This enzyme is critical for viral replication inhibition of HIV RT is therefore an effective mechanism for abrogating infection in patients. 

The answer is d. (Katzung, pp 831-832.) Zidovudine competitively inhibits HIV-1 nucleoside reverse transcriptase. It is also incorporated in the growing viral DNA chain to cause termination. Each action requires activation via phosphorylation of cellular enzymes. Zidovudine decreases the rate of clinical disease progression and prolongs survival in HIV-infected patients. 

An amplification reaction that is used to amplify target RNA or denatured DNA is called the transcription-based amplification system (TAS). This technique involves using an enzyme called reverse transcriptase and a primer with sequence complementary to the sample target RNA molecule in order to synthesize a complementary DNA (cDNA) copy of the sample target RNA. After denaturation to separate the strands, another primer and additional reverse transcriptase are added to synthesize a double-stranded cDNA molecule. Since the first primer has also an RNA polymerase binding site, it can, in the presence of T7 RNA polymerase, amplify the double-stranded cDNA to produce 10 to 100 copies of RNA. The cycle of denaturation, synthesis of cDNA, and amplification to produce multiple RNA copies is repeated. With as few as four cycles, a 2- to 5-millionfold amplification of the original sample RNA target is possible. However, the time required to achieve a millionfold amplification is approximately 4 hours, which is the same amount of time required by PCR. The TAS requires, however, the addition of two enzymes at each cycle and, as such, can be cumbersome. 

Reverse transcriptase is an enzyme that makes a DNA copy of the virus RNA (Step 3). Once made, the DNA enters the cell nucleus and rephcates many times. Another enzyme, the protease, is required to cut the HIV proteins into proper sizes and assemble into the viral particles (Step 7). 

Ge Z, Liu C, Bjorkholm M, Gruber A, Xu D (2006) Mitogen-activated protein kinase cascade-mediated histone H3 phosphorylation is critical for telomerase reverse transcriptase expression/telomerase activation induced by proliferation. Mol Cell Biol 26(l) 230-237 Giet R, Glover DM (2001) Drosophila aurora B kinase is required for histone H3 phosphorylation and condensin recruitment during chromosome condensation and to organize the central spindle during cytokinesis. J Cell Biol 152(4) 669-682... 

Reverse transcriptase is an RNA-dependent DNA polymerase that requires an RNA template to direct the synthesis of new DNA. Retroviruses, most notably HIV, use this enzyme to repHcate their RNA genomes. DNA synthesis by reverse transcriptase in retroviruses can be inhibited by AZT. ddC, and ddl. 

The next stage is to ensure that the recombinant DNA molecule is copied by the enzymes which s)mthesize nucleic acids. These DNA and RNA polymerases synthesize an exact copy of either DNA or RNA from a pre-existing molecule. In this way the DNA polymerase duplicates the chromosome before each cell division such that each daughter cell will have a complete set of genetic instructions which are then passed to the newly formed RNA by RNA polymerase. While both DNA and RNA polymerase require a preformed DNA template, some viruses (such as HIV) have an RNA genome. To duplicate that genome, and incorporate it into a bacterial or mammalian cell, the viruses encode a reverse transcriptase enzyme which produces a DNA copy from an RNA template. 

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