(A) Sequences of the in vitro transcribed RNAs (IR-wtSD2 and IR-mutSD2) used as substrates in the assays shown in (B). The previously mapped 5' end of wild-type espADB mRNA in vivo is underlined. The 5' ends observed for the SD2 mutant in vivo are labeled with a dot. Both substrates have an additional guanosine at the 5' end as a result of transcription initiation by T7 RNA polymerase. G→C substitutions in the mutated SD2 element are indicated.
(B) The RNA substrates, which were monophosphorylated and internally radiolabeled, were treated with equal amounts of purified N-RNase E for the indicated times. Right panel: Treatment with catalytically inactive N-RNase E-D346A, which lacks an essential aspartate residue. Mean values ± SD are shown.