Biochemistry. In the article “Supercoiling-dependent flexibility of adenosine-tract-containing DNA detected by a topological method” by Hua Tsen and Stephen D. Levene, which appeared in number 7, April 1, 1997, of Proc. Natl. Acad. Sci. USA (94, 2817–2822), the authors request that the following correction to Fig. 6 be noted. Due to a printer’s error the revised version of Fig. 6 was not used. A higher-contrast figure and its legend appear below.

Figure 6.

Calculated knot distributions based on the biased slithering model for intramolecular site-specific recombination of a supercoiled Int substrate. Histograms on the left show the distribution of knots obtained for cases in which there are no sequence-dependent preferences for looped regions; profiles on the right correspond to different end-loop biases, ξ, equal to 10, 20, or 30. Model parameters were based on a 4.60-kb DNA substrate divided into 950-bp and 3.65-kb domains. Recombination substrates were considered to be a heterogeneous population of superhelical molecules with mean values of the linking difference corresponding to high (σ = −0.06) or low (σ = −0.03) superhelix density; this heterogeneity was assumed to obey a Gaussian distribution with variances equal to the experimentally measured values obtained from topoisomer distributions of plasmid substrates. Conformations in which a superhelix end loop was partially occupied by the biased DNA segment were weighted according the their elastic energy, as given in Eq. 1.