The molecular biology of intracellular events during Coronavirus infection cycle

CoV-2 which is the causative agent of COVID-19 belongs to genus betacoronaviruses. The sequence analysis of S protein of CoV-2 has shown that it has acquired a ‘polybasic cleavage site’ consisting of 12 aminoacids that has been predicted to enable its cleavage by other cellular proteases possibly increasing its transmissibility. The aminoacids present in receptor binding domain of S protein of SARS CoV which are critical for its binding to cellular receptor are different in CoV-2. The presence of heptanucleotide slippery sequence in ORF1 resulting in ribosomal frameshifting, and presence of transcription regulatory sequences between ORFs resulting in discontinuous transcription, are peculiar features of Coronavirus infection cycle. The exonuclease activity of nsp14 provides possible proofreading ability to RNA polymerase makes coronaviruses different from other RNA viruses allowing coronaviruses to maintain their relatively large genome size. This mini-review summarizes the peculiar features of Coronaviruses genome and the critical events during the infection cycle with focus on CoV-2.