Fig. 1.

Models of strict versus stochastic coupling. (A and B) Scenarios in which transcription and translation are strictly coupled. (A) Genes A and B are cotranscribed, resulting in stoichiometric levels of A and B mRNA (1:1). First-round translation generates equivalent amounts of proteins A and B (1:1, striped symbols), whereas multiple-round translation yields different levels of total proteins (3:1, all symbols). (B) A hypothetical case: Partial reduction of translation rounds yields a product ratio of 2:1 clearly distinct from the original 3:1 ratio. (C) A scenario in which transcription and translation are uncoupled or stochastically coupled. In this case, RNAP has effectively no impact on the lead ribosome, and hence the ratio of protein products made during transcription (3:1, striped symbols) matches that of multiple-round translation (3:1, all symbols).