FIG 3.
Terminator readthrough in vivo is not affected by translation of the leader RNA, but it does require a leader RNA region upstream of the terminator. All data were obtained with agnK12′-lacZ transcriptional fusions. (A) Four cartoons representing the constructs that were tested. The black rectangles represent the lacZ reporter gene, containing its own SD and ATG start site. The promoter +1 transcription start site (arrow) as well as the two agnK12 translational start sites ATG-1 and ATG-2 are indicated. The approximate position of the stem-loop in the leader RNA is also shown. MV781 and MV812 contain a deletion of the terminator stem-loop, from nt +161 to +195. MV747 and MV812 contain a +67A-to-C point mutation, resulting in CTG-1, which is not a translation initiation codon. (B) Deletion of 98 nt immediately upstream of the stem-loop structure leads to termination of transcription. The levels of LacZ expression obtained with agnK12′-lacZ fusions in the presence (MV631) or absence (MV557) of the T1 terminator sequence are indicated.