Extended data 4. Viperin abstracts the 4′-H from CTP.

Using CTP with deuterium (2H denoted with red D) incorporated at either the a, 2′-2H, b, 3′-2H, c, 4′-2H or d, 5′-2H2 (left column), we were able to monitor the loss of deuterium from the resulting product (middle column) and gain of a deuterium in the resulting 5′dA (right column). The 5′dA −m/z increases by one only in reactions containing CTP with a 4′-2H (c, right column). Natural abundance peaks are denoted with dashed vertical lines. All experiments were repeated once.