A, trp leader RNA sequence, showing mutations in the RNase J1 target site. Extent of complementarity of 5′ end-labeled probes to sequences near the 5′ and 3′ ends is indicated. Below the trp leader RNA schematic is shown the wild-type and mutant sequences of the RNase J1 target site. Half-lives of each RNA (min) are shown. The major site of RNase J1 cleavage after nt 101 is indicated by the arrowhead. B–D, Northern blot analysis of wt and mutant trp leader RNA, using probe 1 on low-resolution (B) and high-resolution (D) blots, and probe 2 (C). FL, full-length trp leader RNA. Leftmost lane (M) in B and C contained 5′ end-labeled TaqI fragments of plasmid pSE420 DNA (35), and the sizes of these fragments are indicated on the left. Sequencing ladder in D was generated on M13mp18 single-stranded DNA. Sizes of RNA bands detected by probe 1 in D and discussed in the text are indicated on the right. In B and D, the 101-nt upstream product of RNase J1 cleavage is indicated by the caret.