In vitro inhibition of SerRS. In (A), total calf liver tRNA (3 µg) was aminoacylated with 3H-serine as described in Materials and Methods with various concentrations of SB-217452. In (B), naturally-occurring, purified tRNA[Ser]Sec, purified calf liver tRNASer and tRNA[Ser]Sec, and tRNASer transcripts (0.075 A260 unit) were aminoacylated with 3H-serine in the presence or absence of 20 µM SB-217452. Results shown are counts per minute (CPM) of 3H-serine.