MX1 and infection: Using a more sensitive arrayed format to validate some of our primary screen hits, we found that of four well-studied antiviral effector genes, those for IFITM3, Mx1, PKR, and RSAD2, only the gene for IFITM3 showed an increase in infection compared to the nontargeting guides (Fig. 1C), while guides targeting IFN pathway components gave the expected increase in infection.