IFIT1 and IFIT1B both inhibit the growth of budding yeast (Saccharomyces cerevisiae; top row, middle and right). Co-expressing human Cap1-methyltransferase (which converts cap0-mRNA to cap1-mRNA by adding a methyl group to the first ribose sugar; left) rescued yeast cells expressing IFIT1B (bottom row, right), but not yeast cells expressing IFIT1B (bottom row, middle). Daugherty et al. used this assay to study a wide range of IFIT1/IFIT1B homologs. IFIT: interferon-induced tetratricopeptide repeats.