FIGURE 4.

Test of the hybrid push model, absence of σ. A, fork junction constructs used as DNA templates, natively matched (FJ) or mismatched (MM-FJ) at positions +7 to +9. B, halted 8-mer and 9-mer transcription initiated with pApU, using holoenzyme and core enzyme on fork junction DNA (FJ). C, as in B but halting at position +25. D, percent fall off numbers calculated from B show no abortives at positions +6 and +7 with core polymerase. E, GreB cleavage of halted 8-mer transcription on fork junction (FJ) and mismatched fork junction (FJ-MM) DNA, comparing holoenzyme and core enzyme. In all cases, productive transcription was initiated with pApU (as noted) and labeling was with [α-³²P]ATP.