(A) The population kinetics for the cotranscriptional folding of the pbuE riboswitch under 5.8 pN pulling force and transcription speed 20 nt/s without adenine. There are 8 kinetically important states identified during the folding process, U (Black), C1 (Red), C2 (Blue), C3 (Dark Cyan), C4 (Magenta), C5 (Dark Yellow), C6 (Navy), and T (Wine). (B) The folding pathway inferred from the populational kinetics. The major folding pathway for the pbuE riboswitch under 5.8 pN pulling force and transcription speed 20 nt/s without adenine is U→C1→C3→C5 →C6→T with C2 and C4 as off-pathway kinetic intermediates (traps) connected to U and C3, respectively.