FIGURE 4.

A schematic of the effects of loop forming factors. The coding region of the mRNA is blue (the ribosomes and the poly-A tail are not shown), the noncoding spacers of m and n persistence lengths ɛ are solid black, while the neglected short ends are dashed curves. The loop binding factors are of typical size d. (A) Nonlooped conformations in which the initiation-termination site distribution function is governed by W(r|open). (B) The initiation-termination distribution function in looped configurations is denoted W(r|loop). W(r|loop) is weighted more strongly at small |r| relative to W(r|open). For stronger attraction between loop binding factors the probability of loop formation increases, decreasing the effective distance R that ribosomes must diffuse to be recycled back to the initiation site.