Correction to: Nature Structural and Molecular Biology https://doi.org/10.1038/nsmb.3483, published online 9 October 2017.

In the supplementary information originally posted for this article, the caption for Supplementary Fig. 9a incorrectly stated “The tilt method (Chretien, D. et al., Structure 4, 1031-1040, 1996) uses the position of the tilt axis and shift with tilt of the fringes (2 and 3) in the moiré pattern of 14pf MTs to identify MT polarity. The plus (+) end is oriented towards the top of the page.” Instead of “polarity”, the sentence should have ended with “handedness” and the second sentence should not have been included at all; i.e., the text should read “The tilt method (Chretien, D. et al., Structure 4, 1031-1040, 1996) uses the position of the tilt axis and shift with tilt of the fringes (2 and 3) in the moiré pattern of 14pf MTs to identify MT handedness.” The caption for Supplementary Fig. 9b incorrectly stated “The moiré pattern of a subset of Fourier filtered MT projections also contain an arrowhead pattern, which arises from pf skew, which can be used to corroborate MT polarity (Chretien, D. et al. Structure 4, 1031-1040, 1996). In 14pf MTs, the arrowheads point towards the minus end; black arrowheads indicate the position of the arrowhead moire patterns on the MTs and thus demonstrate that the MTs are oriented with their plus ends towards the top of the image.” In the first sentence, “to corroborate MT polarity” should read “to identify polarity in MTs of known handedness”; in the second sentence, “In 14pf MTs” should read “In left-handed 14pf 3-start MTs”. Thus, the text should read “The moiré pattern of a subset of Fourier filtered MT projections also contain an arrowhead pattern, which arises from pf skew, which can be used to identify polarity in MTs of known handedness (Chretien, D. et al., Structure 4, 1031-1040, 1996). In left-handed 14pf 3-start MTs, the arrowheads point towards the minus end; black arrowheads indicate the position of the arrowhead moire patterns on the MTs and thus demonstrate that the MTs are oriented with their plus ends towards the top of the image.” The errors have not been corrected in the original article.