Molecular model of a plitidepsin molecule (ball and sticks/red and yellow spheres) blocking elongation factor eEF1A (blue) in a eukaryotic ribosome. Ribosomes are the site of protein synthesis in a cell. The large subunit (pink) of the ribosome is bound to transfer ribonucleic acid (tRNA, green), which carries an amino acid, the building blocks of proteins. eEF1A is responsible for bringing transfer RNA to the ribosome. Plitidepsin is a cyclic peptide capable of blocking the synthesis of cytotoxic proteins. This chemical compound is being investigated as an antiviral against RNA viruses, including the SARS-CoV-2 virus, the cause of Covid-19.