Abstract

Arunava Chandra Chandra*, Dr. Dhrubo Jyoti Sen and Dr. Beduin Mahanti

ABSTRACT

COVID-19 is a novel coronavirus with an outbreak of unusual viral pneumonia in Wuhan, China, and then pandemic. Based on its phylogenetic relationships and genomic structures the COVID-19 belongs to genera Betacoronavirus. Human Betacoronaviruses (SARS-CoV-2, SARS-CoV, and MERS-CoV) have many similarities, but also have differences in their genomic and phenotypic structure that can influence their pathogenesis. Coronavirus genome replication and transcription take place at cytoplasmic membranes and involve coordinated processes of both continuous and discontinuous RNA synthesis that are mediated by the viral replicase, a huge protein complex encoded by the 20-kb replicase gene. The replicase complex is believed to be comprised of up to 16 viral subunits and a number of cellular proteins. Besides RNA-dependent RNA polymerase, RNA helicase, and protease activities, which are common to RNA viruses, the coronavirus replicase was recently predicted to employ a variety of RNA processing enzymes that are not (or extremely rarely) found in other RNA viruses and include putative sequence-specific endoribonuclease, 3?-to-5? exoribonuclease, 2?-O-ribose methyltransferase, ADP ribose 1?-phosphatase and, in a subset of group 2 coronaviruses, cyclic phosphodiesterase activities. Although many molecular details of the coronavirus life cycle remain to be investigated, the available information suggests that these viruses and their distant nidovirus relatives employ a unique collection of enzymatic activities and other protein functions to synthesize a set of 5?-leader-containing subgenomic mRNAs and to replicate the largest RNA virus genomes currently known.