Fig. 2.
Premature transcription termination (PTT) depends on various factors. (A) When RNAP pauses during transcription of a natural mRNA that is highly translated, ribosomes occlude Rho from nascent chain rut sites (red) and may facilitate pause escape by “nudging” RNAP forward. Hence, the chances of Rho-dependent PTT are low. (B) When the same gene depicted in panel A contains a nonsense mutation, ribosome traffic is eliminated. This gives Rho access to rut sites (red) and PTT becomes favorable. (C) When RNAP pauses during transcription of a natural mRNA that is normally translated with a low initiation rate, other mechanisms must be employed to prevent Rho-dependent PTT. These likely include RNA structures and omission of rut sites.