Corrections and Clarifications

Abstract

News of the Week: “Appearances can deceive, even with standard reagents” by H. Xin (22 May, p. [997][1]). The reference to a survey conducted with the biweekly magazine Science News should have made clear that the magazine is a Chinese publication unrelated to the U.S. magazine of the same name. Reports: “Remeasuring the double helix” by R. S. Mathew-Fenn et al. (17 October 2008, p. [446][1]). In Fig. 3B and fig. S4, a bending-derived variance estimate was added to the observed variances; it should have been subtracted from the observed variances. The corrected figures show the raw, experimentally observed variances. A corrected version of Fig. 3B and one sentence in the text are provided here. In the supporting online material, similar corrections have been made to fig. S4 and its caption. We thank N. Becker for pointing out these mistakes. ![Figure][1] (B) Observed variance in nanocrystal-nanocrystal separation distance of end-labeled duplexes (circles) and internally labeled duplexes (triangles), plotted with respect to the number of intervening DNA base-pair steps. The variance predictions for an ideal elastic rod with a stretching modulus of 1000 pN (the value measured in single-molecule stretching experiments) are shown (dashed black line) and deviate grossly from the data. A linear relationship between variance and base-pair steps (dashed cyan line, two variables, R 2 = 0.868) is expected if the stretching of base-pair steps is uncorrelated along the DNA duplex (24) . Alternatively, a quadratic relationship (solid black line, two variables, R 2 = 0.989) should hold if the DNA stretches cooperatively. The quadratic fit indicates that each base-pair step contributes 0.21 A of standard deviation to the end-to-end length of a duplex. The y intercept of 5.8 A2 corresponds to variance arising from experimental factors. The variance data points derive from the Gaussian curves in Fig. 2B. The uncertainties in the variance values are estimated to be ±6.6%, based on the standard deviation of repeated measurements for the 25-bp duplex at independent beamlines and with independently prepared samples (fig. S3). The fifth sentence of the third paragraph on page 448 should read, “The data fit a quadratic dependence to within this measurement error (black line; χ2 = 9.95 with 7 degrees of freedom; P = 0.19), but not to a linear dependence (cyan dashed line; χ2 = 62.5 with 7 degrees of freedom; P = 4.8 × 10−11).” [1]: pending:yes