Figure 1: Model of operon coupling by sliding RNAP.

(i) An RNAP molecule (green) terminates transcription of the primary operon (blue), and (ii) starts sliding along the DNA molecule with a diffusion constant D. (iii) While sliding, the RNAP can either dissociate from the DNA with rate k_off, or bind σ⁷⁰ (gray) with rate k_b[σ⁷⁰]. (iv) After binding of σ⁷⁰, the RNAP-σ⁷⁰ complex can either dissociate with a rate k_off,s, or find the promoter (bent arrow) for the secondary operon (pink), which is located is at a distance d along the DNA from the primary operon terminator (T).