FIGURE 2.

Inhibition of TruB and RluA by RNA stem–loops containing f⁵U. TruB is only very modestly inhibited by preincubation with [f⁵U]TSL (open bars); the same degree of inhibition (18%) is seen with two concentrations of [f⁵U]TSL that differ by 10-fold, which is inconsistent with the product stem–loop serving simply as a competitive, noncompetitive, or uncompetitive inhibitor. RluA is inhibited by preincubation with [f⁵U]ASL in essentially stoichiometric fashion (solid bars), which is consistent with irreversible inhibition by the formation of a covalent adduct. The concentrations given are those in the preincubation mixtures, which were diluted 10-fold for the activity assays.