Molecular model of a plitidepsin molecule (red and yellow spheres) blocking elongation factor 1A (eEF1A) in a eukaryotic ribosome (pink). Ribosomes are the site of protein synthesis in a cell. eEF1A (blue) is bound to transfer ribonucleic acid (tRNA, yellow), which carries an amino acid, the building blocks of proteins. This elongation factor is inhibited by plitidepsin, a cyclic peptide capable of blocking the synthesis of cytotoxic proteins. Plitidepsin is being investigated as an antiviral against RNA viruses, including the SARS-CoV-2 virus, the cause of Covid-19.