Blocked transcription-translation complexes are rescued by transcript release followed by trans-translation

Bacterial ribosomes initiate translation while the nascent transcript is still engaged with RNA polymerase, creating a risk that translating ribosomes will become trapped if RNA polymerase is blocked before transcription of the stop codon. Here we show that DNA-binding proteins block RNA polymerase and translating ribosomes in vitro and in vivo. Translating ribosomes are rescued after they trigger release of the nascent transcript from RNA polymerase. Following release of the transcript, ribosomes translate to the 3 end of the mRNA and are rescued by trans-translation. This mechanism allows rescue of all components of blocked transcription-translation reactions.