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Overview of Development of Gene Therapy
Published in Yashwant V. Pathak, Gene Delivery Systems, 2022
Ofosua Adi-Dako, Doris Kumadoh, Yashwant V. Pathak, Nana Kwame Gyamerah
Modified forms of natural viruses and plasmids are among the vectors used in gene therapy (Hardee, Arévalo-Soliz, Hornstein, & Zechiedrich, 2017). Viruses have been changed to replace disease-causing genes with the gene(s) to be transmitted and the sequences that control its expression, while preserving the viral envelope or coat, which promotes transfer (Sauderson, Castro, & Lowenstein, 2013). Plasmids are DNA segments with no natural coat or envelope that can be enclosed in a manufactured lipid membrane or polymer to promote transmission. Commonly used DNA viruses are adeno-associated viruses (AAVs) (a non-pathogenic but abundant tiny virus); adenoviruses (responsible for upper respiratory infections); and herpesviruses. Retroviral vectors produced from lentiviruses (such as human immunodeficiency virus 1 [HIV-1]) and gamma-retroviruses are examples of RNA viruses, which can all integrate a DNA copy of their genetic material into the host genome (Yazdani, Alirezaie, Motamedi, & Amani, 2018).
Classifications of Viruses and Microorganisms
Published in Volodymyr Ivanov, Environmental Microbiology for Engineers, 2020
The established classification includes seven groups of viruses. DNA viruses (groups one and two) include double-stranded and single-stranded DNA viruses. Examples from these groups are viruses causing lysis of bacteria (bacteriophages) as well as oral herpes, chickenpox, and smallpox in humans. RNA viruses (groups three, four, and five) include double-stranded and single-stranded RNA viruses. Examples of these viruses are rotaviruses and enteroviruses, which are major agents of waterborne infections, and viruses causing hepatitis A and C, polio, foot-and-mouth disease, SARS, yellow fever, and influenza. Reverse-transcribing viruses (groups six and seven) are single-stranded RNA viruses (HIV is an example) and double-stranded DNA viruses (hepatitis B virus is an example) replicating using reverse transcription, which is the formation of DNA from an RNA template.
Antiviral Drugs as Tools for Nanomedicine
Published in Devarajan Thangadurai, Saher Islam, Charles Oluwaseun Adetunji, Viral and Antiviral Nanomaterials, 2022
Viruses on the basis of the type of their genome are classified into DNA viruses and RNA viruses. In DNA viruses, viral DNA enters into the host cell nucleus, gets transcribed into mRNA using host cell RNA polymerase, and translates into various virus-specific proteins. The proteins so formed contain some enzymes, which aid in synthesising more viral DNA as well as proteins. Once the virion particles are assembled, these are released by budding or after cell lysis. A retrovirus is a type of virus that has RNA genome; it inserts RNA into the DNA of a host cell, leading to genomic alterations. Within the cytoplasm, the virus uses its reverse transcriptase enzyme and produces DNA from its RNA genome; that is why named as retro (backwards). This new DNA gets incorporated into the host genome by an integrase enzyme. The host cell cannot distinguish it and treats the viral DNA as part of its own genome, resulting in transcription and translation of the integrated viral genes along with its own genes, producing the proteins required to assemble new copies of the virus. Two genes, namely viral genes (v-onc) and cellular genes (c-onc), have been identified, wherein c-onc genes regulate cellular growth (by encoding for growth factors, cellular receptors, signalling and regulatory proteins, DNA binding proteins) and differentiation, but like their viral counterparts, these are mutated. In case of HTLVs, these viruses have a transactivating gene (tax gene), which is essential for replication and transactivates several cellular genes leading to transformation. Such multigenic events occurring result in the development of HTLV-induced leukemia.
New experimental low-cost nanoscience technology for formulation of silver nanoparticles-activated carbon composite as a promising antiviral, biocide, and efficient catalyst
Published in Journal of Experimental Nanoscience, 2022
H. A. Fetouh, H. M. Abd-Elnaby, M. S. Alsubaie, E. R. Sallam
Hepatitis A virus (HAV) is a DNA virus that causes acute hepatitis leading to chronic hepatitis, liver cirrhosis and hepatic cancer. About four hundred millions HAV carriers are infected and more than one million deaths worldwide are reported annually due to HAV-related complications. Effective vaccination of selective antiviral therapeutic drugs alternatives alpha interferon against HAV infection is required. In HAV life cycle, antiviral chemotherapy targets reverse transcription step of pregenome using endogenous viral reverse transcriptase enzyme to incorporate nucleotide analogues in the minus strand of DNA. Nucleotide analogues competitively inhibit reverse transcriptase enzyme. Heterocyclic compounds such as pyrimidine's and diazoles have selective antiviral activities such as Lamivudine, a retroviral inhibitor for HAV replication both in vitro and in vivo. 1-hydroxy-4-nitro-6-trifluoromethyl benzotriazole is an antiviral compound for 12 DNA and RNA viruses including SARS and middle east respiratory syndrome (MERS–CoV) via inactivation of SARS 3CL protease enzyme [9]. However, the synthesis roots for these organic compounds are very complicated and involve various toxic organic compounds [14,16].
The roadmap towards cure of chronic hepatitis B virus infection
Published in Journal of the Royal Society of New Zealand, 2022
The hepatitis B virus is a partially double stranded DNA virus which replicates via a reverse transcriptase. The first effective inhibitors of this enzyme, famciclovir and ganciclovir had poor efficacy and tolerability (intravenous administration, nephrotoxicity). The introduction of lamivudine in 1997 marked a huge advance in the management of HBV. Long-term therapy was associated with maintained viral suppression, alanine aminotransferase (ALT) normalisation, and halt of fibrosis progression and prevention of cirrhosis. Although emergence of antiviral resistance reduced these long-term benefits, the arrival of newer agents with higher barriers to resistance has made life-long therapy a possibility. Several long-term studies have demonstrated that long-term (>5 years) treatment with either entecavir (ETV), tenofovir disoproxil (TDF), or tenofovir alafenamide (TAF) is associated with a reduction in the incidence of decompensation and hepatocellular carcinoma (HCC). Over the last decade, decompensated chronic hepatitis B (CHB) has become a rare indication for elective liver transplantation.
What can we learn from universal Turing machines?
Published in International Journal of Parallel, Emergent and Distributed Systems, 2022
Let us look at the size of a code of a Turing machine, using the encoding defined for the pedagogical universal Turing machine U in (3) and (6), in Section 3.2. As given in Table 2, the code of that tiny universal Turing machine, say N, requires 206 letters in the just mentioned encoding. The code of U itself in the same encoding requires 10,351 letters. That encoding is based on the following alphabet: , considering also the working of U. The genome of a DNA-virus consists in a very long chain of thousands of nucleotides of four kinds: adenine, cytosine, guanine and thyomine denoted by A, C, G and T respectively, given in alphabetic order. In the case of an RNA virus, the composition of the genome is similar: we have also four kinds of nucleotides, the same ones with the exception of thyomine which is replaced by uracil, denoted by U. We later refer to the alphabet A,C,G,U as the RNA-alphabet.