The evolution and the emergence of new mutations of viruses affect their transmissibility and/or pathogenicity features, depending on different evolutionary scenarios of virus adaptation to the host. A typical trade-off scenario of SARS-CoV-2 evolution has been proposed, which leads to the appearance of an Omicron strain with lowered lethality, yet enhanced transmissibility. This direction of evolution might be partly explained by virus adaptation to therapeutic agents and enhanced escape from vaccine-induced and natural immunity formed by other SARS-CoV-2 strains. Omicron’s high mutation rate in the Spike protein, as well as its previously described high genome mutation rate (Kandeel et al., 2021), revealed a gap between it and other SARS-CoV-2 strains, indicating the absence of a transitional evolutionary form to the Omicron strain. Therefore, Omicron has emerged as a new serotype and divergent from the evolutionary lineage of other SARS-CoV-2 strains. Omicron is a rapidly evolving variant of high concern, whose new subvariants continue to manifest. Its further understanding and the further monitoring of key mutations that provide virus immune escape and/or high affinity towards the receptor could be useful for vaccine and therapeutic development in order to control the evolutionary direction of the COVID-19 pandemic.

The natural flavonoid epigallocatechin gallate (EGCG) has a wide range of biological activities including binding to nucleic acids; however, mechanisms of interaction of EGCG with DNA organized in chromatin have not been systematically studied. In this work, interaction of EGCG with chromatin in cells, and with nucleosomes and chromatosomes in vitro was studied using fluorescent microscopy and single particle Förster resonance energy transfer approaches, respectively. EGCG effectively penetrates into the nuclei of living cells and binds to DNA there. Interaction of EGCG with nucleosomes in vitro induces large-scale, reversible uncoiling of nucleosomal DNA that occurs without dissociation of DNA or core histones at sub- and low-micromolar concentrations of EGCG. EGCG does not reduce the catalytic activity of poly(ADP-ribose) polymerase 1 (PARP1), but causes modulation of the structure of the PARP1-nucleosome complex. EGCG significantly changes the structure of chromatosomes, but does not cause dissociation of the linker histone. Reorganization of nucleosomes and chromatosomes by EGCG might facilitate access of protein factors involved in DNA repair, replication and transcription to DNA and thus might contribute to the modulation of gene expression by EGCG that was reported earlier.