Question

1.The novel coronavirus, SARS-Cov2, which is responsible for the disease Covid-19 is a positive strand RNA ((+)ssRNA) virus. From what you learned in BIOL1020, suggest a model of how the SARS-Cov2 genome is replicated. The key enzyme for viral replication is unique to the virus and not found in the human host. What is the name of the enzyme, what is its enzymatic function, and how would you explain that a drug called Remdesivir (an adenosine analogue that causes premature termination of RNA synthesis) is currently the most promising drug against a range of RNA viruses, including Ebola ((-)ssRNA virus), MERS ( (+)ssRNA virus ) and SARS-Cov2 ((+)ssRNA virus)?

2.A mutant E. coli strain is found with a mutation affecting some of its tRNA(Cys). The wild type normally produces a tRNA that recognizes the codon 5’ UGC 3’, and is charged with the amino acid Cysteine (Cys) (its notation is tRNA(Cys)). The mutant tRNA is still charged with Cysteine, but the mutation is in its anticodon that now has the sequence 5’- UCA-3’. How will some of the proteins produced in these E. coli cells be different from the proteins produced in the wild type cells?

Answer 1

1. Coronaviruses contain the largest and most complex RNA genomes, and encode multiple novel replicase nonstructural proteins (nsps).They lack the mechanisms to recognize and correct mutations that arise during genome replication, resulting in a diversity that is required for pathogenesis and adaptation. However, it is not known how viruses encoding large viral RNA genomes of Coronaviridae balance the requirements for genome stability and quasispecies diversity.The mutant viruses of SARS-CoV2 that have stable growth defects and demonstrate an increase in mutation frequency during replication in culture.The limit of replication infidelity during replication of large RNA genomes and how decreased fidelity impacts virus fitness over time are not known.The genetic inactivation of the coronavirus in a nonstructural protein of murine hepatitis virus results in a decrease in replication fidelity.

• Integrase:-It catalyzes the integration of virally derived DNA into the host DNA in the nucleus hence, forming a pro-virus that can be activated to produce viral proteins.

• Remdesivir has shown to reduce symptoms of the disease and lung damage in the early treatment of Covid-19.This anti-viral medication,drug thought to be one of the best prospects for treating Covid-19 but has failed to have any effect in the first full trial It might have potent effects against coronaviruses such as those that cause SARS and MERS. As it became clear that COVID-19 was also caused by a coronavirus which one of the few potentially helpful drugs ready to be in clinical trials.

2.Escherichia coli cells are as a protein factory,despite its extensive knowledge on genetics and molecular biology, there is no a priori guarantee that every gene can be expressed efficiently in this Gram-negative bacterium. Recombinant proteins are used throughout biological and biomedical science. Its production was once the domain of experts, but the development of simple, commercially available systems has made the technology more widespread.So the wild type normally produces a tRNA that recognizes the codon 5' UGC 3'.Factors influencing the expression level include unique and subtle structural features of the gene sequence, the stability and efficiency of mRNA, correct and efficient protein folding, codon usage, degradation of the recombinant protein by ATP-dependent proteases and toxicity of the protein.

• The mutant tRNA is still charged with Cysteine.The objectives of this is to review the potential influence of these different parameters on the yield of recombinant proteins and to provide the reader with practical suggestions allowing optimization of recombinant protein production and targeting to different compartments of the bacterial cell.