Extended Data Figure 4. Inhibition of termination by different size LacR arrays.

(A) Cartoon depicting intermediates detected in the dissolution assay.

(B) To determine the ability of different-sized LacR arrays to inhibit termination, the earliest stage of termination, dissolution (A), was monitored in plasmids containing 0, 12, 16, 32, or 48 lacO repeats. Plasmids were incubated with LacR, and replicated in the presence of [α-³²P]dATP. To measure dissolution, radiolabelled termination intermediates were cut with XmnI. Cleaved products were separated on a native agarose gel and detected by autoradiography.

(C) Quantification of dissolution in (B). When 12 or more lacO repeats were present in the array, dissolution was robustly inhibited for at least 5 minutes. Potent inhibition lasted 10 minutes when 32 lacO sequences were present, and 20 minutes in the presence of 48 lacO sequences. In the absence of lacO sequences, dissolution was essentially complete by 5 minutes. Therefore, 12 lacO repeats are sufficient to inhibit termination for 5 minutes.