Determining the function of IFIT1 using experimental evolution in S. cerevisiae

IFIT (interferon-induced proteins with tetratricopeptide repeats) proteins are important components of the innate immune system that are strongly upregulated when the cell detects viral invasion. IFITs act to inhibit the translation of viral mRNA by binding to the 5’ cap, preventing translation initiation from occurring. Even though IFITs are vital in preventing viral infection, the mechanism of how IFIT1 binds specifically to viral mRNA remains to be poorly understood. Although IFIT1 evolved to inhibit the replication of viruses, it can also inhibit the growth of other organisms like budding yeast (S. cerevisiae) due to their relative lack of mRNA modifications. To examine how IFIT1 inhibits translation, I performed a genetic screen to select for yeast that grew despite the expression of IFIT1. After several rounds of selection, the mutant yeast strains were tested in spotting assays and have developed the ability to evade the growth inhibition effects of IFIT1. The mutant strains show variability in their ability to grow in the presence a plasmid containing IFIT1 and results from cross-testing the strains against IFIT2 suggest that the phenotypes seen in the spotting assays are specific to IFIT1. Sequencing these yeast strains could provide information about which genes can be altered to prevent IFIT1 from inhibiting translation and that information can then be used to determine what the mechanism of ‘non-self’ sensing and translation inhibition by IFIT1